“This supplement to the U.S. Energy Information Administration’s (EIA) U.S. Crude Oil and Natural Gas Proved Reserves, 2013 ranks the 100 largest U.S. oil and gas fields by their estimated 2013 proved reserves. EIA defines a field as “an area consisting of a single reservoir or multiple reservoirs all grouped on, or related to, the same individual geological structural feature and/or stratigraphic condition. There may be two or more reservoirs in a field that are separated vertically by intervening impervious strata or laterally by local geologic barriers, or by both.” This definition is not used by all states in their designation of fields; consequently, areas classified as individual fields by some states may be found combined in these tables or in the EIA Field Code Master List.”