Snecma is the prime contractor for the development of the storable and cryogenic liquid rocket engines of the Ariane launcher, including the Viking storable engine, HM7 cryogenic engine, Vulcain and Vulcain 2 cryogenic engines. The new cryogenic engine Vinci is under development and qualification is planned by 2006. This paper presents the results of a study which has been performed over the last 2 years to define the most suitable engines for the future versions of expendable launchers as well as future reusable vehicles. A family of new engines is introduced including LOX/LH2 engines and LOX/CH4 engines. Particularly, a cryogenic staged combustion fuel-rich engine has been designed and optimized in two versions. The first one is dedicated to an expendable launcher and could be developed first. It offers high performance and reliability at the minimum cost. The second version is a derivative which offers reusability and increased performance for future RLV application. The development and production of the expandable version will allow to achieve and demonstrate high reliability and to better evaluate the potential for reusability through the development test campaigns which usually requires as many as 20 tests with the same engines. Only some critical components would be changed to achieve reusability. This approach allows to minimize the development cost and to keep the production cost low for both versions by using a learning curve over a large number of engines.