Crude oil production in Texas doubled over the past three years to hit 3 million barrels a day in April for the first time since the late 1970s, nearly the amount that Iraq produces and 36 percent of total U.S. oil production, according to recent data from the U.S. Energy Information Administration.

Iraq, the second-largest producer in the Organization of Petroleum Exporting Countries, produced a little over 3 million barrels a day in April, according to OPEC’s May 2014 oil market report.

Elsewhere in the U.S., North Dakota’s oil production topped 1 million barrels a day in the same month for the first time in history, nearly tripling its production over three years, EIA said in its monthly petroleum supply report. The two oil-producing states accounted for nearly half of the country’s total crude production in April, 8.4 million barrels a day.

texascrude Chart from the U.S. Energy Information Administration, Drilling Productivity Report Photo: EIA

While the rest of the country’s oil production grew at only 2 percent annually over the last three years, production volumes in Texas grew an average 28 percent and in North Dakota, 37 percent. The third-largest source of oil in the U.S. is the Gulf of Mexico, but production there declined from 27 percent to 17 percent of the country’s total over the same period.

The gains in Texas came from unconventional tight oil and shale plays in the Eagle Ford, Western Gulf Basin and Permian Basin, regions where the controversial drilling method hydraulic fracturing, or fracking, has developed quickly.

North Dakota’s production growth comes from its Bakken shale, also a tight oil reservoir, which has caused a boom in crude-by-rail transport that has led to several deadly accidents.