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Sustainability 2011, 3, 1866-1887; doi:10.3390/su3101866
sustainability
ISSN 2071-1050
www.mdpi.com/journal/sustainability
Article
A New Long Term Assessment of Energy Return on Investment
(EROI) for U.S. Oil and Gas Discovery and Production
Megan C. Guilford
1
, Charles A.S. Hall
1,2,
*, Pete O’ Connor
3
and Cutler J. Cleveland
3
1
Department of Environmental Studies, State University of New York, College of Environmental
Science and Forestry, Syracuse, NY 13210, USA; E-Mail: mcguilfo@syr.edu
2
Program in Biology and Environmental Sciences, State University of New York, College of
Environmental Science and Forestry, Syracuse, NY 13210, USA
3
Department of Geography and Environment, Boston University, Boston, MA 02215, USA;
E-Mails: paoconn@bu.edu (P.O.C.); cutler@bu.edu (C.J.C.)
* Author to whom correspondence should be addressed; E-Mail: chall@esf.edu;
Tel.: +1-315-147-016-870; Fax: +1-315-470-6934.
Received: 5 June 2011; in revised form: 1 August 2011 / Accepted: 6 August 2011 /
Published: 14 October 2011
Abstract: Oil and gas are the main sources of energy in the United States. Part of their
appeal is the high Energy Return on Energy Investment (EROI) when procuring them. We
assessed data from the United States Bureau of the Census of Mineral Industries, the
Energy Information Administration (EIA), the Oil and Gas Journal for the years 1919–2007
and from oil analyst Jean Laherrere to derive EROI for both finding and producing oil and
gas. We found two general patterns in the relation of energy gains compared to energy
costs: a gradual secular decrease in EROI and an inverse relation to drilling effort. EROI
for finding oil and gas decreased exponentially from 1200:1 in 1919 to 5:1 in 2007. The
EROI for production of the oil and gas industry was about 20:1 from 1919 to 1972,
declined to about 8:1 in 1982 when peak drilling occurred, recovered to about 17:1 from
1986–2002 and declined sharply to about 11:1 in the mid to late 2000s. The slowly
declining secular trend has been partly masked by changing effort: the lower the intensity
of drilling, the higher the EROI compared to the secular trend. Fuel consumption within
the oil and gas industry grew continuously from 1919 through the early 1980s, declined in
the mid-1990s, and has increased recently, not surprisingly linked to the increased cost of
finding and extracting oil.
OPEN ACCESS
Sustainability 2011, 3 1867
Keywords: EROI; oil; gas; depletion; energy cost
1. Introduction
Petroleum, including crude oil, natural gas, and natural gas liquids, is industrialized society’s most
important fuel. Since its discovery in the United States in 1859, the use of petroleum has increased
rapidly in both absolute terms and relative to other fuels. It accounted for about two thirds of total fuel
use in the 1970s [1]. Since the oil crises of the 1970s, many entities within the United States have
attempted to devise alternatives to oil. Nevertheless we consume today about the same proportion of
petroleum as in the 1970s. As the easier-to-find and exploit resources are increasingly depleted, we
have to turn to other, more difficult and expensive resources. The deep water Gulf of Mexico
exploration and exploitation efforts are but one example. Getting oil from these more difficult
environments is more expensive, and any oil company will tell you that the easy oil is gone.
It takes energy as well as money to produce energy. One important issue pertaining to petroleum
availability in the United States is Energy Return on Investment (EROI), the ratio of energy returned
compared to the energy used to get it. A more energy-intensive process of production, other things
being equal, results in a lower energy return on energy (and dollar) investment. In theory, EROI takes
into consideration all energies produced and all energies consumed to get that production. In practice,
EROI is usually calculated from the direct and indirect energy used to produce a given amount of
energy Murphy et al. in press [2].
The U.S. oil and gas industry is traditionally the most energy-using industry in the United States,
and the energy intensity of getting energy did not escape the notice of M. King Hubbert, the most
important analyst of oil production patterns in the United States, who mentioned it in his notes for his
deposition before the 93rd U.S. Congress. However, few or no analysts attempted to quantify that
relation until Hall and Cleveland undertook this analysis in 1981 [3]. They concluded that the energy
found per foot of all types of drilling while seeking and producing oil and gas declined from about 50
barrels of oil (including gas on an energy basis) in 1946 to about 15 in 1978. They also found that the
energy cost increased from about 0.1 to 2 barrels equivalent per foot. EROI was not calculated
explicitly in that paper, but one can infer that the EROI implied by these data declined during that
period from at least 50:1 to about 8:1. They also found that while the (inferred) EROI declined over
time it was greatly influenced by the amount of drilling, and that a large amount of drilling effort in
any given year was associated with a low EROI relative to the secular trend and the converse.
Previously Davis had reported on a similar relation for return per drilling effort [4]. An update to the
Hall and Cleveland study was published by Cleveland in 2005 [5] that estimated that the EROI for oil
and gas for the United States had declined from a peak of about 30:1 in 1972 to about 13:1 in 1982,
during a period of very intense drilling, but that the ratio had recovered to about 18:1 in 1997. He also
found that if corrections were made for the quality of the different fuels the ratio had declined from
20:1 to about 11:1 from 1954–1997. Since the data that have been analyzed previously covered only a
short time span (1946–1977 or 1954–2002 at best) our objective is to analyze the data, including
Sustainability 2011, 3 1868
earlier and more recent data for a longer time span using a consistent methodology. We also compared
the energy return on investment for both finding oil and producing it.
2. Methods
We derived a series of 13 point estimates for the EROI for U.S. oil and gas at mostly five-year
intervals over the past 90 years. We did this for both discovery and for producing oil and gas. In each
case the energy equivalent of the oil and gas found or produced was dividing by the sum of energy
values of the estimates of the direct and indirect energy used in that year to produce that energy. We
consider oil and gas together as the data on inputs are aggregated that way. While some of the
petroleum produced or found for a given year came from past investments, and some of today’s
investments will not be reflected in production for a number of years, we believe this technique
appropriate because most of the energy used in an oil field goes for pumping and pressurizing fields,
so is related to contemporary production.
There are three analyses reported in this paper:
1. Oil and Gas discoveries: undertaken by Guilford and Hall;
2. Oil and Gas production undertaken by Guilford and Hall and independently by O’Connor and
Cleveland, and considered preliminary.
When Guilford and Hall finished their analysis they found that O’Connor and Cleveland had begun
the same analysis with some different assumptions. We include their preliminary analysis here as a
sensitivity analysis of our own.
2.1. Methods to Derive EROI for Oil and Gas Discovery
We calculated the EROI of discovery of oil and gas from:
Equation:
EROI =
Mean quantity of energy discovered from oil and gas activities
Quantity of energy used in that activity
Numerator:
We derived a five-point mean value of oil and gas discoveries (i.e., mean of discoveries for the year
in question and the two years before and two years after each year analyzed) from 1919 to 2007.
Barrels of oil and barrels of oil equivalent of gas discovered were converted into GJ by multiplying by
6.118 GJ/BOE. Discovery data was supplied courtesy of Jean Laherrere (Table 3).
Denominator:
There is no clear procedure to derive how much of total effort is used for discovery and how much
for development and production. In general about one third of the feet drilled are for exploratory, not
development wells
2
. But drilling is only part of the effort, and other uses of energy (e.g., pumping and
pressurizing) are more concentrated in production. We estimated energy used by the exploratory wells
from dollar cost data from 1992 to 2006 from John S. Herold
[5]
by dividing exploratory dollar costs by
Sustainability 2011, 3 1869
total costs (exploratory + developmental + production). We estimated energy used to find (vs. develop
or produce) oil and gas by the average of the above quotient 16%, multiplied by the total energy use.
EROI for Oil and gas production (by Guilford and Hall):
Both groups compiled data sets of the direct and indirect energy used for producing oil and gas for
the United States from official government sources including publications and websites. We all
calculated EROI from the following equation:
EROI =
Quantity of Energy Supplied from oil and gas produced
Quantity of Energy used in that activity
Numerator:
We all used production data (total energy gained through production) for the United States from
two data sources: the Energy Information Administration [1] and the production summary table from
the Oil and Gas Journal and from online versions of each last issue of February from 1978 and earlier
until 2010 in print at Cornell University (Table 5). We then converted the raw physical units of output
to Joules using the conversion factors from Table 1.
Table 1. Conversion values from physical or energy units to Joules (from MIT Department
of Physics, Energy info card/Physics of energy version 8.21).
Units
Conversion
1 barrel of Oil Equivalent
5.8 × 10E6 BTU = 6.118 GJ
1 kilowatt-hour (kWh)
3.6 MJ
1 BTU
1.055 kJ = 1,055 J
1 barrel of oil (bbl)
42 gallons= 5.615 cubic feet = 159.0 liters
Gasoline
121.3 MJ/gal ( 32.1 MJ/L or 43.1 MJ/kg or 115 mBTU/gal)
Crude Oil 6.119 GJ/bbl = 5.8 mmBTU/bbl or 39.7 mmBTU/ton
or 145.7 MJ/gal or 38.5 MJ/L or 43.8 MJ/kg (=GJ/ton)
1 cubic foot of natural gas
1,008 to 1,034 BTU
1 therm of natural gas
100,000 BTU = 98 cubic feet
1 gallon of crude oil
138,095 BTU = 145.7 MJ
1 barrel of crude oil
5.8 Mega BTU = 6.1 MJ
1 gallon of residual fuel oil
149,690 BTU = 158 GJ
1 gallon of gasoline
125,000 BTU = 132 GJ
Denominator:
Guilford and Hall estimated oil and gas industry-specific energy costs from data from the United
States Bureau of the Census of Mineral Industries from 1919 to 2007 (Tables 5 and 6). The
publications of the Census of Mineral industries are in print until only 1992. More recent data were
derived from the Energy Information Administration (EIA) website as well as the online version of the
Census of Mineral Industries. There were major changes in their format, but we believe we interpreted
the new data correctly. In some few cases, as identified in A-1, we had to make educated guesses.
More specifically, we used summary tables from the Census of Mineral Industries (CMI) from 1919
to 1992 for on-site energy use. The Bureau of the Census of Mineral Industries publishes data every
Sustainability 2011, 3 1870
five years; however the criteria used to organize the data changed periodically, especially for 1997 and
following, sometimes making it very difficult to interpret their tables. For example, the online version
of the CMI, which was used for more recent data, is in a different format than the print version for
years in which they overlap (e.g., 1992). CMI continues to supply estimates of physical quantities of
natural gas (the most important fuel) used, but for some reason (apparently “insufficient data quality”),
it gives the quantity of oil only in monetary terms subsequent to 1992, which we converted to physical
quantities from mean annual price Appendix (A-1). Electricity is electricity not generated on site but
purchased. We next converted these raw physical units (barrels, billion cubic feet, kilowatt-hours, etc.)
into Joules using conversion factors from Table 1.
Indirect (offsite) energy costs were derived by multiplying inflation-corrected expenditures for
capital goods and materials bought by the oil and gas industry by a factor approximating the energy
intensity of the oil and gas industry expenditures (14 MJ/$ per 2005 dollar [6]) with a sensitivity
analysis using a low estimate (8.3 MJ/$, the mean energy use for the society as a whole) and high
energy use (20 MJ/$ for the oil and gas industry [6]). After 1972 the energy associated with producing
and supplying these indirect costs often were higher than the direct use (A-1, in Appendix,
summarized in Table 3). We then summed all of these energy values from the direct and indirect
energy costs to give a total energy cost. This is equivalent to the standard assessment (EROI
st
)
recommended by Murphy et al. in press [2].
After converting the raw physical units of both the energy costs and gains to energy we divided the
total energy gains (finding or production data) by the total direct and indirect energy cost (fuel
consumed) to calculate an EROI value for each year at five-year intervals from 1919 to 2007. Annual
drilling intensity data (exploratory plus production, in million feet per year) is from the Energy
Information Administration [1] website.
2.2. Difficulties with Missing Data
Generally the Census of Mineral Industries (CMI) gave quite complete energy cost analyses,
especially in the middle years of this analysis, but sometimes, and increasingly in recent years, data
was omitted for direct energy consumption in order to “avoid disclosing proprietary information”. In
some cases CMI stated energy expenditures for specific fuels, in others CMI stated dollar energy
expenditures, and in a few cases no inference from expenditures was possible. The inferences of
missing values are uncertain, but we present them here as a secondary analysis.
Where CMI gave only dollar amounts for specific fuels within some sub-sectors, we used monetary
costs by multiplying adjacent energy dollar rankings to derive the physical quantities consumed.
Where sub-sectors had quantities reported but no price associated, we used EIA price series (annual
averages) to determine the dollar value. Occasionally neither expenditures nor quantities were
available for self-use of natural gas, so we interpolated as best we could.
We assumed that self-use of natural gas in the Natural Gas Liquid (NGL) Extraction sub-sector in
2007 was proportional to the electricity consumption in that sector, at the same ratio as in 2002.
Therefore, we estimated that because electricity use decreased 14.5% from 2002 to 2007, the amount
of natural gas for “self-use” was 14.5% below 2002 levels. This is a fairly large value, equal to 30% of
the gas consumed in that year, and it is relatively uncertain. As it is self-use, no cost information is
Sustainability 2011, 3 1871
available to make a better estimate. Self-use of crude petroleum is seen in the Petroleum and Natural
Gas Extraction sub-sector for 1992 and 1997, but no values are reported for 2002 or 2007. However,
this is a small fraction of energy use, accounting for less than 1% of overall energy use in 1992 and
1997. Therefore, we have not attempted to estimate self-use of crude petroleum. Note that
consideration of self-use of natural gas raises the issue of whether to look at “External Energy Return”
(EER) or “Net Energy Return” (NER). We assume that there is an opportunity cost to using the natural
gas in most cases of domestic oil production, and so include self-use in our EROI, making it an NER
analysis. It would be omitted for an EER analysis, leading to a higher value for EROI.
Where specific energy quantities were unknown, but the total energy expenditures were known, we
distributed the unaccounted-for energy among the various unknown categories equal to the distribution
in nearby years. The amount of energy so distributed never exceeded 7% of total energy cost. For
example, in 2002, the “Support Services” sub-sector listed neither expenditures nor quantities for
natural gas, nor for residual and heavy diesel. There was $93,311,000 in energy costs unaccounted for
in that sub-sector. We divided the residual cost among the two fuels based on their 2007 ratio, with
47.5% going to residual and heavy diesel, and 52.5% going to natural gas. We then used total price
data from EIA to determine the quantities of those fuels consumed.
A considerable amount of energy is categorized as either “other” (possibly including minor fuels
such as petroleum coke), or “undistributed” (reported by small firms on a shorter survey form). These
range from 8–16% of total energy consumption over the years 1992–2007. We assumed that these
other fuels were natural gas and added them to gas, as natural gas represents the overwhelming
majority of known direct energy consumption by the “other” and “undistributed” fuels. This increases
the direct energy consumption slightly compared to the case in which these expenditures are
distributed among the various energy resources, because natural gas is the least expensive per BTU of
the fuels used over the period 1992-2007. The total effect of these assumptions is shown in Table 2.
Table 2. Changes in Direct Energy using Alternative Analysis.
Year Fuel type
Original
Value
Alternative
Value
Calculation
1992
Natural gas
878 Bcf
1,042 Bcf
Included “other” and “undistributed” fuels as natural gas
1997
Natural gas
1,072 Bcf
1,207 Bcf
Included “other” and “undistributed” fuels as natural gas
2002 Natural gas 876 Bcf 1,018Bcf
Inferred missing values for support and drilling natural
gas consumption from expenditures;
Included “other” and “undistributed” fuels as natural gas
2002 Fuel oil 30 Mbbl 9.0 Mbbl
Inferred from known total energy expenditures and
known price of fuel oil
2002 Gasoline 100 M gal 71.8 M gal
Inferred from known gasoline expenses and average cost
for that year
2007 Natural gas 633.2Bcf 1183Bcf
Added estimate of339 Bcf of self-use in the NGL
Extraction sub-sector;
Calculated 160.3 purchased (all sectors) on known price;
Included “other” and “undistributed” fuels as natural gas
2007 Fuel oil 9.03 Mbbl 14.05 Mbbl
Inferred from known total energy expenditures and
known price of fuel oil
2007 Gasoline 100 M gal 211 M gal
Inferred from known gasoline expenses and average cost
for that year
Sustainability 2011, 3 1872
For capital expenditures, O’Connor and Cleveland’s analysis uses the current-cost depreciation
series from the Bureau of Economic Analysis for Sector 2110, Oil and Gas Extraction, rather than the
capital expenditures from the CMI. The use of the depreciation series produces the changes seen in
Table 3, below.
Table 3. Changes in Capital Expenditures for Alternative Analysis.
Year
Capital expenditures
($M, nominal)
Depreciation
($M, nominal)
1972
3,456
3,433
1977
12,944
8,969
1982
42,216
27,141
1987
11,717
20,868
1992
12,520
22,506
1997
25,152
25,051
2002
28,781
38,110
2007
125,460
84,010
2.3. Avoidance of Double-Counting
For materials and supplies, the Census of Mineral Industries is used as in the primary analysis, but
the series is corrected to eliminate the feedstock inputs. The natural gas liquids extraction sector
purchases large amounts of natural gas as a feedstock, not as a fuel; it extracts the liquids and then sells
both of the products. Because the energy involved in producing the gas has already been accounted for
in the “direct energy inputs,” it is not appropriate to include it as a material expenditure for calculating
indirect energy inputs. Therefore, we subtract the estimated proportions of natural gas feedstocks from
the cost of materials purchased by the sector. For the years 1972–1982, the specific cost of natural gas
feedstocks was not available, so we applied feedstock’s share of NGL materials cost in 1987–2007 to
the known NGL materials cost for 1972–1982. The feedstock represents about 43% of total materials
expenditures (all sub-sectors) over the period 1972–2007. The effect is shown in Table 4.
Table 4. Correction for Subtracting Feedstock.
Year
Materials
($M, nominal)
Without Feedstock
($M, nominal)
1972
9,471
5,555
1977
31,694
18,004
1982
89,370
57,934
1987
44,032
24,087
1992
44,092
21,788
1997
49,157
29,981
2002
48,032
25,683
A second issue of possible double-counting could not be easily avoided. The Census of Mineral
Industries includes “Contract Work” in the overall category of “Total Cost of Supplies”. If a company
within the sector outsources work to another company in the sector, the energy use of the contractor is
Sustainability 2011, 3 1873
already included in the direct energy consumed by the sector. It would then be inappropriate to apply
the indirect emissions factor of 14 MJ/$ to the Contract Work, and the “Total Cost of Supplies” would
have to be reduced by this amount. On the other hand, if the contracting company does not report to
CMI in the oil and gas production sector (perhaps it is a general engineering firm, an engine
manufacturer, a road-building firm, or some other sort of company), then it is appropriate to apply the
indirect emissions factor. However, we have not yet identified a means to separate the Contract Work
into work done by companies in this sector and work done by companies not in this sector. The
analysis at present includes the “Total Cost of Supplies” without removing the within-sector Contract
Work, and so likely overstates this indirect energy cost. “Contract Work” is roughly 20% of “Total
Cost of Supplies” in 1997, 2002, and 2007. If half of the contract work was double-counted, then the
actual indirect energy would be reduced by about 10%, and so the actual total energy inputs would be
reduced by perhaps 5% (if indirect energy were half of all energy).
The three major changes we made in the empirical data set from CMI are then:
(1) Missing values are inferred for direct energy consumption, and “other” and “undistributed”
fuels are included for 1992–2007;
(2) Depreciation series from BEA are used instead of CMI for capital; and, CMI data series for
materials were corrected to eliminate NGL feedstock. The cumulative effect of these three
changes is given in “sensitivity analysis”, below.
3. Results
EROI for discoveries declined sharply from over 1200 to 1 for 1919 to 5:1 in 2007 (Figure 1 and
Table 5). EROI for production of the oil and gas industry (with no quality corrections) were about 20:1
from 1919 to 1972, declined to about 8:1 in 1982, when peak drilling occurred, recovered to about
17:1 during low drilling years 1986–2002 and declined sharply to about 11:1 in the mid-late 2000s
(Figure 2). There is an inverse relation between the energy return on investment and the drilling rates
so that after 1957 EROI tends to be higher when the drilling rate is lower (Figure 3 and 3b).
Figure 1. EROI for discoveries for the U.S. Oil and Gas Industry. The inset is the same
data plotted on a different scale.
0
200
400
600
800
1000
1200
1400
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
EROI
Year
Sustainability 2011, 3 1874
Table 5. Estimates of energy costs, gained and EROI associated with energy discovered by
the U.S oil and gas industry. Oil and gas discovered courtesy of Jean Laherrere.
Year
Direct +
Indirect Total
Exploration/total
cost average %
Direct +
Indirect Total
Exploration
Discovery
(GJ)
EROI
1919
171
0.16
26.87
33.04
1229.48
1939
567
0.16
89.10
26.31
295.26
1954
1096
0.16
172.23
10.52
61.10
1958
1652
0.16
259.60
8.14
31.34
1963
1859
0.16
292.12
3.98
13.61
1972
2378
0.16
373.68
4.34
11.62
1977
3826
0.16
601.22
3.30
5.50
1982
5345
0.16
839.91
2.88
3.42
1987
2779
0.16
436.69
4.22
9.67
1992
2463
0.16
387.04
1.84
4.74
1997
2860
0.16
449.42
3.18
7.08
2002
2548
0.16
400.39
3.55
8.86
2007
3569
0.16
560.83
2.81
5.02
Figure 2. EROI for production for the U.S. Oil and Gas Industry. Column two is total energy
costs, and column four is estimated costs for discovery alone.
y = -0.0859x + 185.25
R² = 0.2547
0
5
10
15
20
25
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
EROI
Year
Sustainability 2011, 3 1875
Figure 3. EROI and drilling intensity for same year. Note inverse relation, especially after
1957 between drilling rate and EROI. Increased drilling does not necessarily generate more
oil produced because the EROI decreases with high drilling efforts after 1958.
Figure 4. EROI vs. drilling intensity for same year.
Energy input: The input of energy is dominated by the energy required to make equipment and then
natural gas used on site. There was a sharp peak in 1982 following the price increases of the 1970s and
a second, smaller peak in 2007 (Figure 5 and Table A-1 in Appendix).
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
20
25
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Drilling Intensity (Million Meters)
EROI
Year
Drilling Intensity
EROI
y = -0.0262x + 17.409
R
2
= 0.0384
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50
EROI
Million Meters Drilled
EROI
Linear (EROI)
Sustainability 2011, 3 1876
Figure 5. Energy consumed within the U.S. oil and gas industry (Data from the U.S.
Bureau of Census of Mineral Industries). Data summarized in Table 6.
Table 6. Estimates of energy costs, gained and EROI associated with energy produced by
the U.S. oil and gas industry.
Year
Energy Gains
(Production)
Total (EJ)
Direct Energy
Total (PJ)
Indirect Energy
Total (PJ)
Direct +
Indirect Total
Production
EROI
1919
2.70 139.2 32.0 171 15.79
1939
11.31 488.0 79.0 567 19.93
1954
25.98 53.9 193.0 1096 23.72
1958
29.19 991.0 661.0 1652 17.68
1963
35.28 1091.2 768.0 1859 18.99
1972
47.17 1435.3 943.0 2378 19.85
1977
41.29 1812.4 2013.0 3826 10.79
1982
41.33 1618.6 3727.0 5345 7.73
1987
40.44 1437.6 1342.0 2779 14.54
1992
40.03 1361.5 1101.0 2463 16.24
1997
40.66 1595.0 1265.0 2860 14.23
2002
38.75 1336.2 1212.0 2548 15.23
2007
37.99 1084.6 2485.0 3569 10.65
3.1. Sensitivity Analysis of Results
Energy output: The production of oil and gas increased from 422 million barrels oil equivalent
(BOE) in 1919 to a peak of 3,517 in 1970 and then declined to 1,811 in 2008. We compared EIA and
Oil and Gas Journal of production data and they were not significantly different (Figure 6).
0.0
1.0
2.0
3.0
4.0
5.0
6.0
1919
1939
1954
1958
1963
1972
1977
1982
1987
1992
1997
2002
2007
EJ
Year
Gas
Oil
Electric
Indirect
Sustainability 2011, 3 1877
Figure 6. U.S. Oil and Gas Production (Megabarrels of oil equivalent/day). Data from the
Energy Information Administration and Oil and Gas Journal. 10 million barrels of oil per
day equivalent translates to 22.3 Exajoules per year.
The greater direct energy consumption in the alternative analysis (caused by inferring values where
CMI data is missing) partially offsets the reduced indirect energy consumption (caused by removing
the natural gas feedstock from the materials purchased by the NGL sector). The resulting EROI is
similar to, but slightly higher than, the EROI found in our original analysis.
The energy intensity (i.e., the energy associated with each dollar spent for indirect expenditures is
not known with certainty. One can derive a value of 14.5 MJ used per 2005 dollar spent from the
Carnegie-Mellon Green energy web site for oil and gas exploration and discovery. We used a value of
8.3 MJ/$ (average for the entire society for a minimum estimate, and a value of 20 MJ/$ (average for
direct and indirect for the U.S. and UK oil and gas industry for 2005 [6] for an upper limit (Figure 7).
This sensitivity analysis indicates a maximum difference of a little more than a factor of two. Since the
indirect costs are about half of total costs these uncertainties would add no more than a little more than
25% uncertainty to the final EROI values. Since the middle value seems much the most likely the
actual uncertainty is less than this.
We also undertook an “extreme” sensitivity analysis by comparing our results with a completely
independent assessment undertaken (without our knowledge) by O’Connor and Cleveland (Figure 8)
The results suggest very similar patterns and, generally values, except that O’Connor and Cleveland’s
values are about 15–25% higher for the 1970s and early 1980s. Much of this difference appears due to
their use of depreciation vs. Guilford and Hall’s use of capital expenditures for indirect cost estimates
(Table 3).
0
1
2
3
4
5
6
7
8
9
10
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
MBOE/ day
Year
OGJ
EIA
Sustainability 2011, 3 1878
Figure 7. Sensitivity Analysis for indirect energy consumed by the U.S. oil and gas industry.
Figure 8. Sensitivity Analysis comparison with the independent analysis of O’Connor and
Cleveland. Note that the values for O’Connor and Cleveland do not exactly match those in
Table 7, as that table simply shows the effect of the three most significant differences in
methodology. Several other minor differences also exist.
0
1000
2000
3000
4000
5000
6000
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Peta Joules
Year
8.3 MJ/$
20 MJ/$
0
5
10
15
20
25
1950 1960 1970 1980 1990 2000 2010
EROI
Year
Guilford & Hall
O'Connor & Cleveland
14
MJ/$
Sustainability 2011, 3 1879
Table 7. Changes in Alternative Analysis 1972–2007.
Original
Alternative
Year Output
(EJ)
Direct
(PJ)
Indirect
(PJ)
EROI %
Indirect
Direct
(PJ)
Indirect
(PJ)
EROI %
Indirect
1972
47.17
1435.3
943
19.8
39.7%
1435.3
654
22.6
31.3%
1977
41.29
1812.4
2013
10.8
52.6%
1812.4
1208
13.7
40.0%
1982
41.33
1618.6
3727
7.7
69.7%
1618.6
2382
10.3
59.5%
1987
40.44
1437.6
1342
14.5
48.3%
1437.6
1070
16.1
42.7%
1992
40.03
1361.5
1101
16.2
44.7%
1426.6
868
17.4
37.8%
1997
40.66
1595.0
1265
14.2
44.2%
1630.1
925
15.9
36.2%
2002
38.75
1336.2
1212
15.2
47.6%
1380.5
982
16.4
41.6%
2007
37.99
1084.6
2485
10.6
69.6%
1554.9
1546
12.3
49.9%
One of our reviewers was especially interested in the possible time lag effect—that drilling at one
point in time might produce oil at a later time. We investigated this by slipping the production relative
to the investment. The results showed no particular change in the basic patterns of EROI over time
although it decreased somewhat the inverse relation between effort and EROI (Figure 9).
Figure 9. Time lag in the EROI value five years after the drilling occurred. An inverse
correlation is still present between the EROI and the drilling intensity (effort).
4. Discussion
Oil and gas production has been decreasing steadily since its peak in 1970 and a second, smaller
peak in 1985 when Alaska came on line (Fig.4). The maximum production in 1970 was about
9 million barrels equivalent per day. Data from the EIA and the Oil and Gas Journal show that the
most recent production is roughly 5 million barrels equivalent per day, with an increasing proportion
being gas. The U.S EROI has fluctuated over time but there is an overall negative trend over time,
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
20
25
1900 1920 1940 1960 1980 2000 2020
Drilling Intensity
(Million Meters)
EROI
Year
EROI
Drilling million meters
EROI
Drilling Intensity
Sustainability 2011, 3 1880
especially since 1950 (Figure 1). The reason that EROI is dropping is because the finding and
production of oil is steadily decreasing and our energy investment is increasing. Gas production has
remained approximately flat, mostly due to unconventional resources replacing faltering conventional
resources. The remarkably high EROI for finding oil and gas in early years contributed to significant
increases in GDP and probably had a great deal to do with a tremendous increase in wealth in the first
part of the 20th century, as well as to the development of systems based on inexpensive and abundant
petroleum. Its steep decline is equally remarkable.
A higher demand for oil, sometimes driven by falling supplies, increases prices, which encourages
more drilling, but ironically more drilling does not mean that more oil and gas will be found. There is a
clear inverse correlation between EROI and drilling rates (Figure 3a). It appears likely that petroleum
supplies will continue to diminish no matter how much money is invested into drilling. It is possible
for production to increase even as EROI decreases, as happened, for example, over the period
1950–1970. However, the U.S. has been in a long period of decreasing EROI and decreasing
production, suggesting that depletion has more importance than technology. The EROI has a shape
similar to the Hubbert curve (although tilting to right) and confirms that we are most definitely in the
second half of the age of oil for U.S domestic oil supply (Figure 2). Most direct energy used is natural
gas in oil and gas production, and since oil but not gas needs considerable energy to pump or
pressurize the formation, it is likely that natural gas is subsidizing oil production and that the EROI for
oil alone would be much lower.
We checked the sources of the data for the numerator (energy gains) and the denominator (energy
inputs) of the EROI equation throughout our study. We found that most of the data was not too
difficult to find until 1992. Post 1992 there have been many different formats and tables for the fuel
consumed within the oil and gas industry, which made our assessment more difficult. A more
disturbing trend is that over time the data sets are less complete. Given the critical trends we see and
the need to continue these analyses this is a very disturbing finding. Recent funding cutbacks for the
U.S. Energy Information agency are likely to contribute to a further decline in data quality and quality
as that information becomes far more critical.
We conducted numerous sensitivity analyses which took into consideration different indirect energy
costs, an independent preliminary EROI study from O’Connor and Cleveland and a time lag in
response to drilling intensity and EROI. Indirect energy costs are not known with certainty since the
excellent earlier work at the University of Illinois was disbanded decades ago. We took into
consideration different quality energy corrections and used 14 MJ/$ for our analysis, a value defensible
from the Carnegie-Mellon site (2002 data corrected for inflation to 2005) and also by correcting for
inflation earlier values from the University of Illinois studies (Figure 7). We used 14 MJ/$ for
comparison purposes with previous studies. None of the uncertainty assessment patterns or even values
for EROI over time changed in any significant way (i.e., usually much less than about 25%) our basic
results.
There are sources of energy that may delay the beginning of the end of cheap oil. Unconventional
sources of oil such as tar sands, natural gas extraction through hydraulic fracturing and off shore
drilling may add to our supply of energy but will probably be expensive once the “cream” is skimmed
from the sweet spots. Technology has not alleviated the problem of decreasing EROI and may not be
able to do that in the future as depletion of highest quality resources continues. Thus society probably
Sustainability 2011, 3 1881
faces a continuing decline in the EROI of both conventional oil and gas. The EROI of most
alternatives to conventional hydrocarbons is also low, so that the EROI of the future seems unlikely to
be high enough to support society as a whole in the format we are familiar with [7].
5. Conclusion
As time goes on, domestic oil production continues to decline while energy exploitation efforts
increase as the easy oil and gas is depleted. The age of cheap oil is coming to an end. The decreasing
EROI of the oil industry is a factor contributing to the end of cheap oil. The EROI for production for
the United States’ oil industry dropped from roughly 24:1 in 1954 to 11:1 in 2007. Over time more
energy is used to find and produce the same or less petroleum. Depletion tends to lead to lower
petroleum production, but it also gives incentives for increased exploration, both of which contribute
to a diminishing EROI. Demand for oil and gas has tended to increase steadily over time, which in turn
accelerates both drilling and further depletion. The EROI is a reflection of the efficiency within a
given system. As the EROI of domestic oil and gas, the nation’s most important fuel supplies,
continues to drop off it makes a sustainable society increasingly difficult. We must adjust to this new
reality by using less, rather than expanding drilling efforts.
Acknowledgements
We thank Susan Bucci of the Bureau of Census for helping us through the maze of the Census’
data, Doug Hansen for helping to improve the wording, and two anonymous reviewers. We thank
Mason McMahon for early help with obtaining and graphing data. We would like to thank Jean
Laherrere for the data he supplied us to derive EROI for both finding and producing oil and gas.
Special note from the first author: I would like to thank my parents for their support and always
encouraging me to strive to do my best.
References and Notes
1. Energy Information Administration (EIA). Official Energy Statistics from the U.S. Government.
Publisher: Available online: http://www.eia.doe.gov (accessed on 4 May 2010).
2. Murphy, D.; Hall, C.A.S.; Dale, M.; Cleveland,C. Order from chaos: A preliminary protocol for
determining the EROI of fuels. Sustainability, in press.
3. Hall, C.A.S.; Cleveland, C.J. Petroleum drilling and production in the United States: Yield per
effort and net energy analysis. Science 1981, 211, 576-579.
4. Davis, W. A study of the future productive capacity and probable reserves of the U.S. Oil Gas J.
1958, 56, 105-119.
5. Cleveland, C.J. Net energy from the extraction of oil and gas in the United States. Energy 2005,
30, 769-782.
6. Gagnon, N.; Hall, C.A.S.; Brinker, L. A preliminary investigation of energy return on energy
investment for global oil and gas production. Energies 2009, 2, 490-503.
7. Hall, C.A.S.; Balogh, S.; Murphy, D.J. What is the minimum EROI that a sustainable society
must have? Energies 2009, 2, 25-47.
Sustainability 2011, 3 1882
Appendix
Table A-1. Raw data and calculations used for estimating energy costs for U.S. oil and
gas industry. Values in yellow are rough interpolations or extrapolations based on
neighboring years.
Year
Type
Raw
value(#)
Original Units
(M= 10^6)
Conversion
To Metric
(or other)
Units
Energy
Density
Total
Energy
Units
1919 N. Gas 100 Bcf 0.028 2.8 E9m^3 36 101 PJ
1919 Fuel oil 5.9 Mbbls
6.118
(GJ/bbl) 36 PJ
1919 Gasoline 1.9 Mgal 42 0.045 Mbbls
6.118
(GJ/bbl) 0.277 PJ
1919 Electric 285
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 1 PJ
1919
Electric
(QC) 285
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 2 PJ
1919 Capital
200 Mdollars 11.3 2259 2005 8.3 MJ/$ 19 PJ
1919 Capital *
200 Mdollars 11.3 2259 2005 14 MJ/$ 32 PJ
1919 Capital
200 Mdollars 11.3 2259 2005 20 MJ/$ 45 PJ
1919 TOTLO - - - - - - 157 PJ
1919 TOTAL * - - - - - - 170 PJ
1919 TOTQC * - - - - - - 171 PJ
1919
TOTHIQC
- - - - - - 184 PJ
1939 N. Gas 462.1 Bcf 0.028 12.9388 E9m^3 36 466 PJ
1939 Fuel oil 2.2 Mbbls
6.118
(GJ/bbl) 14 PJ
1939 Gasoline 17.7 Mgal 42 0.42 Mbbls
6.118
(GJ/bbl) 3 PJ
1939 Electric 651.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 2 PJ
1939
Electric
(QC) 651.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 6 PJ
1939 Capital 399.8 Mdollars 14.1 5619.2 2005 8.3 MJ/$ 47 PJ
1939 Capital * 399.8 Mdollars 14.1 5619.2 2005 14 MJ/$ 79 PJ
1939 Capital 399.8 Mdollars 14.1 5619.2 2005 20 MJ/$ 112 PJ
1939 TOTLO - -
- - - - 531 PJ
1939 TOTAL * - - - - - - 563 PJ
1939 TOTQC * - - - - - - 567 PJ
1939
TOTHIQC
- - - - - - 600 PJ
1954 N. Gas 842.4 Bcf 0.028 23.5872 E9m^3 36 849.1 PJ
1954 Fuel oil 4603 Mbbls
6.118
(GJ/bbl) 28.2 PJ
Sustainability 2011, 3 1883
Table A-1. Cont.
Year
Type
Raw
value(#)
Original Units
(M= 10^6) Conversion
To Metric
(or other) Units
Energy
Density
Total Energy Units
1954
Gasoline - Mgal 42 - Mbbls
6.118
(GJ/bbl)
- PJ
1954
Electric 2748
M(kWh)
(=GWh) kWh
3.6
TJ/kWh
9.9 PJ
1954
Electric
(QC) 1314
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh
25.7 PJ
1954
Capital 1896.4 Mdollars 7.3 13767.9 2005
8.3
MJ/$ 114 PJ
1954
Capital * 1896.4 Mdollars 7.3 13767.9 2005 14 MJ/$
193 PJ
1954
Capital 1896.4 Mdollars 7.3 13767.9 2005 20 MJ/$
275 PJ
1954
TOTLO - - - - - - 1001 PJ
1954
TOTAL * - - - - - - 1080 PJ
1954
TOTQC * - - - - - - 1096 PJ
1954
TOTHIQC
- - - - - - 1178 PJ
1958
N. Gas 894.3 Bcf 0.028 25.0404 E9m^3 36 901 PJ
1958
Fuel oil 5.7 Mbbls
6.118
(GJ/bbl)
35 PJ
1958
Gasoline 100.0 Mgal 42 2.38 Mbbls
6.118
(GJ/bbl)
15 PJ
1958
Electric 4275.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh
15 PJ
1958
Electric
(QC) 4275.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh
40 PJ
1958
Capital 6993.5 Mdollars 6.8 47237.9 2005
8.3
MJ/$ 392 PJ
1958
Capital * 6993.5 Mdollars 6.8 47237.9 2005 14 MJ/$
661 PJ
1958
Capital 6993.5 Mdollars 6.8 47237.9 2005 20 MJ/$
945 PJ
1958
TOTLO - - - - - - 1358 PJ
1958
TOTAL * - - - - - - 1628 PJ
1958
TOTQC * - - - - - - 1652 PJ
1958
TOTHIQC
- - - - - - 1936 PJ
1963
N. Gas 964.2 Bcf 0.028 26.9976 E9m^3 36 972 PJ
1963
Fuel oil 5.5 Mbbls
6.118
(GJ/bbl)
34 PJ
1963
Gasoline 157.6 Mgal 42 3.75 Mbbls
6.118
(GJ/bbl)
23 PJ
1963
Electric 6696.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh
24 PJ
1963
Electric
(QC) 6696.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh
63 PJ
Sustainability 2011, 3 1884
Table A-1. Cont.
Year
Type
Raw value(#)
Original Units
(M= 10^6) Conversion
To Metric
(or other) Units
Energy
Density Total Energy
Units
1963
Capital 8596.1 Mdollars 6.4 55015.0 2005 8.3 MJ/$ 455 PJ
1963
Capital * 8596.1 Mdollars 6.4 55015.0 2005 14 MJ/$ 768 PJ
1963
Capital 8596.1 Mdollars 6.4 55015.0 2005 20 MJ/$ 1097 PJ
1963
TOTLO - - - - - - 1508 PJ
1963
TOTAL * - - - - - - 1820 PJ
1963
TOTQC * - - - - - - 1859 PJ
1963
TOTHIQC
- - - - - - 2188 PJ
1972
N. Gas 1164.0 Bcf 0.028 32.592 E9m^3 36 1173 PJ
1972
Fuel oil 18.9 Mbbls
6.118
(GJ/bbl) 115 PJ
1972
Gasoline 122.9 Mgal 42 2.93 Mbbls
6.118
(GJ/bbl) 15 PJ
1972
Electric 14060.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 51 PJ
1972
Electric
(QC) 14060.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 132 PJ
1972
Capital 12927.2 Mdollars 5.2 67221.4 2005 8.3 MJ/$ 559 PJ
1972
Capital* 12927.2 Mdollars 5.2 67221.4 2005 14 MJ/$ 943 PJ
1972
Capital 12927.2 Mdollars 5.2 67221.4 2005 20 MJ/$ 1347 PJ
1972
TOTLO - - - - - - 1913 PJ
1972
TOTAL * - - - - - - 2297 PJ
1972
TOTQC * - - - - - - 2378 PJ
1972
TOTHIQC
- - - - - - 2782 PJ
1977
N. Gas 1382.0 Bcf 0.028 38.696 E9m^3 36 1393 PJ
1977
Fuel oil 33.1 Mbbls
6.118
(GJ/bbl) 203 PJ
1977
Gasoline 223.4 Mgal 42 5.32 Mbbls
6.118
(GJ/bbl) 33 PJ
1977
Electric 19679.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 71 PJ
1977
Electric
(QC) 19679.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 184 PJ
1977
Capital 44638.3 Mdollars 3.2 142842.6 2005 8.3 MJ/$ 1194 PJ
1977
Capital * 44638.3 Mdollars 3.2 142842.6 2005 14 MJ/$ 2013 PJ
1977
Capital 44638.3 Mdollars 3.2 142842.6 2005 20 MJ/$ 2876 PJ
1977
TOTLO - - - - - - 2893 PJ
1977
TOTAL * - - - - - - 3712 PJ
1977
TOTQC * - - - - - - 3826 PJ
1977
TOTHIQC
- - - - - - 4688 PJ
Sustainability 2011, 3 1885
Table A-1. Cont.
Year Type Raw value(#)
Original Units
(M= 10^6) Conversion
To Metric
(or other) Units
Energy
Density
Total Energy
Units
1982 N. Gas 913.0 Bcf 0.028 25.564 E9m^3 36 920 PJ
1982 Fuel oil 52.6 Mbbls
6.118
(GJ/bbl)
322 PJ
1982 Gasoline 343.5 Mgal 42 8.18 Mbbls
6.118
(GJ/bbl)
50 PJ
1982 Electric 34857.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh
125 PJ
1982
Electric
(QC) 34857.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh
326 PJ
1982 Capital 131585.1 Mdollars 2 263170.2 2005
8.3
MJ/$ 2209 PJ
1982 Capital* 131585.1 Mdollars 2 263170.2 2005
14 MJ/$
3727 PJ
1982 Capital 131585.1 Mdollars 2 263170.2 2005
20 MJ/$
5324 PJ
1982 TOTLO - - - - - - 3627 PJ
1982 TOTAL* - - - - - - 5144 PJ
1982 TOTQC* - - - - - - 5345 PJ
1982
TOTHIQC
- - - - - - 6942 PJ
1987 N. Gas 1011.4 Bcf 0.028 28.31 E9m^3 36 1019 PJ
1987 Fuel oil 20.8 Mbbls
6.118
(GJ/bbl)
127 PJ
1987 Gasoline 174.8 Mgal 42 4.16 Mbbls
6.118
(GJ/bbl)
25 PJ
1987 Electric 28418.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh
102 PJ
1987
Electric
(QC) 28418.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh
266 PJ
1987 Capital 55749.0 Mdollars 1.7 94773 2005
8.3
MJ/$ 795 PJ
1987 Capital* 55749.0 Mdollars 1.7 94773 2005
14 MJ/$
1342 PJ
1987 Capital 55749.0 Mdollars 1.7 94773 2005
20 MJ/$
1917 PJ
1987 TOTLO - - - - - - 2069 PJ
1987 TOTAL* - - - - - - 2616 PJ
1987 TOTQC* - - - - - - 2779 PJ
1987
TOTHIQC
- - - - - - 3354 PJ
1992 N. Gas 878.0 Bcf 0.028 24.584 E9m^3 36 885 PJ
1992 Fuel oil 9.6 Mbbls
6.118
(GJ/bbl)
59 PJ
1992 Gasoline 82.7 Mgal 42 1.97 Mbbls
6.118
(GJ/bbl)
12 PJ
Sustainability 2011, 3 1886
Table A-1. Cont.
Year
Type Raw value(#)
Original Units
(M= 10^6) Conversion
To Metric
(or other) Units
Energy
Density Total Energy
Units
1992
Electric 33036.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 119 PJ
1992
Electric
(QC) 33036.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 309 PJ
1992
Capital 56544.1 Mdollars 1.4 79161.7 2005 8.3 MJ/$ 653 PJ
1992
Capital * 56544.1 Mdollars 1.4 79161.7 2005 14 MJ/$ 1101 PJ
1992
Capital 56544.1 Mdollars 1.4 79161.7 2005 20 MJ/$ 1574 PJ
1992
TOTLO - - - - - - 1728 PJ
1992
TOTAL * - - - - - - 2176 PJ
1992
TOTQC * - - - - - - 2366 PJ
1992
TOTHIQC
- - - - - - 2839 PJ
1997
N. Gas 1072.0 Bcf 0.028 30.016 E9m^3 36 1081 PJ
1997
Fuel oil 11.2 Mbbls
6.118
(GJ/bbl) 69 PJ
1997
Gasoline 164.0 Mgal 42 3.90 Mbbls
6.118
(GJ/bbl) 24 PJ
1997
Electric 34,339.8
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 124 PJ
1997
Electric
(QC) 34,339.8
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 321 PJ
1997
Capital 74309.0 Mdollars 1.2 89170.8 2005 8.3 MJ/$ 750 PJ
1997
Capital * 74309.0 Mdollars 1.2 89170.8 2005 14 MJ/$ 1265 PJ
1997
Capital 74309.0 Mdollars 1.2 89170.8 2005 20 MJ/$ 1807 PJ
1997
TOTLO - - - - - - 2047 PJ
1997
TOTAL * - - - - - - 2562 PJ
1997
TOTQC* - - - - - - 2759 PJ
1997
TOTHIQC
- - - - - - 3302 PJ
2002
N. Gas 876.0 Bcf 0.028 24.528 E9m^3 36 883 PJ
2002
Fuel oil 30.0 Mbbls
6.118
(GJ/bbl) 184 PJ
2002
Gasoline 100.0 Mgal 42 2.38 Mbbls
6.118
(GJ/bbl) 15 PJ
2002
Electric 27255.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 98 PJ
2002
Electric
(QC)
27255.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 255 PJ
2002
Capital 78518.0 Mdollars 1.1 86369.8 2005 8.3 MJ/$ 718 PJ
2002
Capital* 78518.0 Mdollars 1.1 86369.8 2005 14 MJ/$ 1212 PJ
2002
Capital 78518.0 Mdollars 1.1 86369.8 2005 20 MJ/$ 1731 PJ
Sustainability 2011, 3 1887
Table A-1. Cont.
Year
Type
Raw
value(#)
Original Units
(M= 10^6) Conversion
To Metric
(or other) Units
Energy
Density Total Energy
Units
2002
TOTLO - - - - - - 1898 PJ
2002
TOTAL* - - - - - - 2391 PJ
2002
TOTQC* - - - - - - 2548 PJ
2002
TOTHIQC
- - - - - - 3067 PJ
2007
N. Gas 770.0 Bcf 0.028 21.56 E9m^3 36 776 PJ
2007
Fuel oil 9036.0 Mbbls
6.118
(GJ/bbl) 55 PJ
2007
Gasoline 100.0 Mgal 42 2.38 Mbbls
6.118
(GJ/bbl) 15 PJ
2007
Electric 25496.0
M(kWh)
(=GWh) kWh
3.6
TJ/kWh 92 PJ
2007
Electric
(QC) 25496.0
M(kWh)
(=GWh) 2.6
Fossil Fuel
Equiv. kWh
3.6
TJ/kWh 239 PJ
2007
Capital 188518.0 Mdollars 0.94 177207 2005 8.3 MJ/$ 1473 PJ
2007
Capital * 188518.0 Mdollars 0.94 177207 2005 14 MJ/$ 2485 PJ
2007
Capital 188518.0 Mdollars 0.94 177207 2005 20 MJ/$ 3550 PJ
2007
TOTLO - - - - - - 2411 PJ
2007
TOTAL * - - - - - - 3423 PJ
2007
TOTQC * - - - - - - 3569 PJ
2007
TOTHIQC
- - - - - - 4634 PJ
TOTLO = the total sum of the direct energy plus the lower calculated indirect energy estimate (8.3
MJ) and not electric quality corrected.
Total* = the total sum of direct energy plus the middle value of indirect energy (14 MJ) and not the
quality corrected energy value.
TOTQC* = the total sun of direct energy values plus the middle value of indirect energy (14 MJ) and
includes quality corrected electric values.
TOTHIQC = the total sum of direct energy values plus the highest calculated indirect energy cost (20
MJ) and includes quality corrected electric values.
© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
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