A number of companies have held oil concessions, but commercial deposits were not discovered until July 1984, when the US-based Hunt Oil Company struck oil in the eastern governorate (province) of Marib. As of 1999, Yemen had two aging refineries. The capacity of the Aden refinery had declined from 170,000 barrels per day before the 1994 civil war to 120,000 barrels per day as of 2002. The newer Marib plant has a capacity of 10,000 barrels daily. Oil production is split between Canadian Occidental (which had been operating in North Yemen since 1987) in the Masillah block, US Hunt Oil in the Marib field, and three other operators. In 2001, oil production amounted to 452,521 barrels per day. Proven oil reserves as of 1 January 2002 were 4 billion barrels. Exploration declined in 1994 due to civil war between the north and south but picked up again in 1997.
Most exploration occurs in the Marib and Masillah fields, with some activity also in the eastern Hadhramaut an Hehara regions. Most new oil discoveries in recent years have been in southern Yemen.
With natural gas reserves estimated in early 2002 at 478 billion cu m (17.2 trillion cu ft), Yemen has potential as a gas producer. Most of the known reserves are concentrated in the Marib-Jawf fields, operated by the Yemen Exploration and Production Company.
Total electricity production was 2.8 billion kWh in 2000, of which 100% was from fossil fuels. Total installed capacity in 2001 was 810,000 kW, entirely based on conventional thermal sources.