Crude oil reserves in the U.S. grew for the fourth straight year, reaching the highest level since 1976, according to an Energy Department report released Thursday.
The report says reserves grew 4.5 billion barrels, or 15 percent, to 33 billion barrels in 2012. It was the biggest one-year jump since 1970.
The U.S. consumed 6.9 billion barrels of crude-based fuels last year.
Drillers have learned how to unlock oil trapped in rock formations once thought too expensive to tap, using horizontal drilling and hydraulic fracturing, a process known as fracking. North Dakota and Texas, home to the two most prolific of these formations, accounted for the vast majority of the increase.
The oil reserves reported represent crude that can likely be produced in the future with current technology and prices.