The Bighorn Basin contains 134 oil fields that produce (or have produced) from 60 reservoirs and/or co-mingled reservoirs ranging in age from Cambrian to Paleocene. Nine fields within the Bighorn Basin are in the top 25 producing fields in Wyoming. Seven of these rank in the state's top ten producing fields. (Wyoming Enhanced Oil Recovery Institute, 2011). Oil and gas production in the Bighorn Basin has steadily declined over the last 35 years. Although the Bighorn Basin produced 11.5 million barrels of oil in 2013, accounting for 18.3 percent of Wyoming's total oil production, it is a 31 percent decrease from 2000 oil production levels, a 59 percent decrease from 1990 production, and an almost 77 percent decrease from 1978 (WOGCC, 2014). Natural gas production in the basin has similarly decreased 48 percent from 1978 production levels (WOGCC, 2014).