Oklahoma. Production in Oklahoma has more than doubled since 2005 to more than 128 million barrels in 2014, pushing its way into the top five of the most productive oil-producing states. Oklahoma is the intersection of many of the largest national pipelines.
With oil production increasing by 1,000% between 2003 and 2015, North Dakota has 5.7 billion barrels of proven reserves and produced 397 million barrels in 2014. When combined with output from Texas, the two states provide half the entire U.S. oil output.