U.S. Holds More Oil Than Saudi Arabia or Russia, Rystad Energy Says
http://www.bloomberg.com/news/articles/2016-07-05/u-s-holds-more-oil-than-saudi-arabia-or-russia-rystad-energy-saysJuly 5, 2016

For the U.S. more than 50 percent of the remaining oil reserves is in unconventional shale oil. Texas holds more than 60 billion barrels of shale oil according to the new data.
New data from Rystad distinguishes between reserves in existing fields, in new projects and potential reserves in recent discoveries and in yet undiscovered fields. An established standard approach is applied to all fields in all countries, said Rystad, which means reserves can be compared apples-to-apples across the world. Other public sources are based on official reporting from national authorities, which are in turn based on diverse and opaque standards, Rystad said.

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Note that this is essentially wishful thinking, not discovered oil.