World Crude Oil Reserves by Year. Loading Crude Oil Proven Reserves Definition: Oil reserves are the amount of technically and economically recoverable oil. Reserves may be for a well, for a reservoir, for a field, for a nation, or for the world. This is a list of countries by proven oil reserves. Proven reserves are those quantities of petroleum which, by analysis of geological and engineering data, can be estimated, with a high degree of confidence, to be commercially recoverable from a given date forward from known reservoirs and under current economic conditions. Some statistics on this page are disputed and controversial. Different sources give different figures. Some of the differences reflect different types of oil included. Diffe Total U.S. oil reserves in 2017 exceeded a brief, one-year, 47-year-old record, highlighting the importance of crude oil development in shales and low permeability plays, mainly in the Southwest. The new record for natural gas extends a longer-term trend of development, mainly in shale plays in the Northeast.