Domestic oil production grew last year by the highest margin since the federal government started keeping records in 1900.

Crude oil output averaged 8.7 million barrels per day, an increase of 1.2 million barrels per day, which is the largest increase since record-keeping began, the Energy Information Administration (EIA) reported Monday.

{mosads}The EIA attributed the record increase to tight oil from shale formations.

“Most of the increase during 2014 came from tight oil plays in North Dakota, Texas, and New Mexico where hydraulic fracturing and horizontal drilling were used to produce oil from shale formations,” the EIA said in a report.

The agency expects production to increase in 2015 and 2016, although not to the same degree as 2014, it said.

“Since mid-2014, the price of crude oil has fallen about 50 percent, which has slowed production in marginal drilling areas and focused investment in the more developed areas of tight oil plays,” the EIA said in its report.

On a percentage basis, crude production grew 16.2 percent in 2014, the highest rate since 1940.

While unconventional drilling techniques are bringing historically high rates of production, 2014 did not set a new record in crude output.

But the United States produces the most oil of any country after outpacing Saudi Arabia last year.