Global shale resources are vast enough to cover more than a decade of oil consumption, according to the first-ever U.S. assessment of reserves from Russia to Argentina.
The U.S. Department of Energy estimated "technically recoverable" shale oil resources of 345 billion barrels in 42 countries it surveyed, or 10 percent of global crude supplies. The department had previously only provided an estimate for U.S. shale reserves, which it on Monday increased from 32 billion barrels to 58 billion.
The pace of oil and gas production gains has consistently surprised forecasters since horizontal drilling and hydraulic fracturing, better known as "fracking", were pioneered in U.S. shale rock formations about ten years ago. Only the U.S. and Canada were producing oil and natural gas from shale in commercial quantities, the department said.
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Monday's assessment indicated that Russia has the largest shale oil resource, with 75 billion barrels. Russia and the U.S. were followed by China at 32 billion, Argentina at 27 billion and Libya at 26 billion.
The report said gas from shale formations increased world natural gas resources by 47 percent to 22,882 trillion cubic feet.
The question of whether other countries can replicate North America's success in drilling in shale rocks has captivated geologists and diplomats. U.S. crude imports are at a 16-year low, reconfiguring the map of global oil trade.
"Looking at shale resources has typically been understated by outside market participants because the geology is new and the technology is growing rapidly," said Edward Morse, head of commodities research at Citigroup.
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Production from shale has helped keep a lid on crude oil prices at about $120 a barrel, giving western countries leverage to impose sanctions on Iran, a key supplier. World oil demand is about 90 million barrels a day, suggesting the world shale oil resource covers 10.5 years of consumption.
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The U.S. and Canada have advantages including large domestic pipeline networks. Both countries also have enough water and specialized drilling rigs to support fracking, which involves pumping huge quantities of liquid and sand underground to crack open rocks and release energy reserves.
Private U.S. landowners also have rights to hydrocarbons beneath their properties. According to Mr Morse, this situation is "truly unique to the United States" and makes oil and gas exploration more efficient.
The U.S. report looked only at technically recoverable resources without regard to profitability, and warned the estimates are "highly uncertain".
Adam Sieminski, head of the department's Energy Information Administration, said: "Today's report indicates a significant potential for international shale oil and shale gas, though the extent to which technically recoverable shale resources will prove to be economically recoverable is not yet clear."
Prospective shale areas including formations beneath large oilfields in the Middle East and the Caspian Sea region were left out of the assessment.
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The International Energy Agency said in its five-year oil market forecast last month: "Although uncertainties remain, it is impossible to ignore the possibility that current non-conventional technologies, as they spread and get both perfected and mainstreamed, could lead to a wholesale reassessment of global reserves."
The new U.S. estimate of world shale gas resources at 7,299 trillion cubic feet is 10 percent higher than a previous estimate made in 2011.
Inside the U.S., shale now constitutes 30 percent of oil and 40 percent of natural gas production, the department said.