The mainland US holds enough oil trapped in shale rock reserves to meet its import needs for seven years, according to a new government report that puts a figure on the fastest-growing source of new crude.
About 24 billion barrels of "technically recoverable" oil is trapped in the Lower 48 states, it said, more than half of that in a California basin that has thus far been less successful than booming frontiers in North Dakota and Texas.
The report, the first ever commissioned by the US Energy Department to quantify the amount of oil in shale structures, offers staggering figures: considered nearly impossible to tap until a few years ago, shale oil may now account for over 20% of the onshore oil resources in the contiguous United States.
Shale oil is making up an ever-greater portion of the domestic crude coming to market.
Liquids-rich shale plays, coupled with benchmark oil prices near multi-year highs around $100 per barrel, have prompted a drilling renaissance, luring not only the largest domestic oil companies like ExxonMobil but also foreign giants like China's CNOOC and Norway's Statoil to the long-neglected US oil patch.
"The (reserve) numbers continue to move upward, especially as oil prices remain strong," Brian Lively, at energy investment bank Tudor Pickering Holt in Houston, told Reuters.
The report, commissioned by the Energy Department (DoE) and prepared by research firm Intek, identifies prospects like the Bakken shale in the northern US plains as holding as much as 3.65 billion barrels of technically recoverable oil resource.
With shale oil, the United States has an estimated 114 billion barrels of recoverable resources, excluding Alaska and offshore reserves. But, by comparison, proven deposits are a much smaller 20.7 billion barrels.
"A lot of things such as price and future technology will determine how much shale oil actually gets out of the ground," Matt Marshall, senior energy analyst at Bentek Energy, told Reuters.
Proponents including ExxonMobil and EOG resources, among the largest US shale drillers, say rising shale production could further help shed reliance on foreign oil, but detractors want proof that the drilling technique is safe.
Due to rising domestic output, and an economic slowdown, the US has been importing significantly less crude in recent years. Last year, it imported 9.16 million barrels per day, down almost 10% from a peak in 2005.
Oil from shale helped the country boost crude and liquids production by 3% last year to 7.51 million bpd, the highest in nearly a decade.
A majority of the oil shale resources are located in California's Monterey/Santos shales which have about 15.42 billion barrels, the report said.
Occidental Petroleum, the major player in the Monterey shale, says it has about 560 million barrels of proved oil reserves there.
The report also identified the Bakken shale formation in North Dakota and Montana as one of the richest US plays.
Bakken has propelled US oil domestic production in recent years and oil companies produced as much as 350,000 bpd in North Dakota fields in April, three times more than in 2007.
Further south, the Eagle Ford play in Texas has 3.35 billion barrels of oil resources and 20.8 trillion cubic feet of natural gas, the report said.
All told, the report also identifies 750 Tcf of technically recoverable natural gas resources in the contiguous lower 48 states.
Natural gas production from shale rock has itself tripled between 2007 and 2009, and the potential gas resource identified on Friday represents around a hundred years of US supply.