Sexual economics theory assumes that heterosexual communities can be analyzed as marketplaces in which men offer women resources such as love, respect, money, and commitment in exchange for sex. In response to economic, political, and other disadvantages, women collectively restrict their sexuality to maintain a low supply relative to male demand, thereby ensuring a high price. Hence, we tested the hypothesis that sexual norms and practices would be more restrictive in countries marked by gender inequality than in countries where the genders were more equal. An international online sex survey (N>317,000) yielded four measures of sexual activity, and 37 nations' means on all four measures were correlated with independent (World Economic Forum) ratings of gender equality. Consistent with predictions, relatively high gender equality was associated with more casual sex, more sex partners per capita, younger ages for first sex, and greater tolerance/approval of premarital sex.