U.S. to Be Biggest Global Oil Producer by 2020

America will overtake Saudi Arabia as the world's largest petroleum producer by about 2020 because of the U.S. boom in extracting oil from shale, according to the International Energy Agency.

The Paris-based agency's 2012 World Energy Outlook predicts that sharply higher oil and gas output and increased vehicle efficiency will make America "all but self-sufficient" in energy by 2035. The U.S. currently imports about one-fifth of the energy it consumes.

The IEA also expects the U.S. to overtake Russia as the leading global producer of natural gas by 2015 and become an exporter of the fuel by 2020.

Oil and natural gas are extracted from shale by a process called hydraulic fracturing, or "fracking," in which large amounts of chemicals, sand and water are pumped into the ground under high pressure. The process is controversial because of concerns that the chemicals involved could contaminate ground water.

The U.S. will boost crude output, including oil extracted by fracking, from 8.1 million barrels per day in 2011 to an estimated 11.1 million bpd by 2020, according to the IEA. That would compare with an expected 10.6 million bpd for Saudi Arabia. By 2030, North America is likely to be a net exporter of oil, the group forecasts.