U.S. exports of petroleum products reached a record in August for the month as refiners boosted rates, the American Petroleum Institute said.

Shipments of fuels increased to 4 million barrels a day last month, up 7.5% from a year earlier, the industry- funded group said recently in a monthly report. Refiners operated at the strongest seasonal level in August, raising gasoline production to the highest on record for the month.

Fuel exports averaged 3.96 million barrels a day this year through August, up 17% from 2013, according to the API. Refineries processed 16.7 million barrels a day of crude last month, up 2.3 percent from a year ago and the highest August level.

Total deliveries of petroleum products, a measure of consumption, climbed 1% from a year earlier to 19.3 million barrels a day. Gasoline demand slid 1.2% to 9.02 million. Output of the motor fuel averaged 9.77 million, up 4.6% and the highest level for the month.

“Petroleum demand last month showed slow but steady growth,” John Felmy, chief economist at the API in Washington, said in the report. “Domestic crude and refinery production also remained quite strong.”

Demand for distillate fuel, which includes diesel and heating oil, climbed 2.7% from a year earlier to 3.79 million. Jet fuel consumption rose 2.3% to 1.56 million.

Deliveries of residual oil, used for commercial and industrial heating, electricity generation and ship propulsion, dropped 64% to 149,000 barrels a day.

Crude production jumped 16% from 2013 to 8.61 million barrels a day. Output has surged as a combination of horizontal drilling and hydraulic fracturing, or fracking, has unlocked supplies trapped in shale formations, including the Bakken in North Dakota and the Eagle Ford in Texas.

Imports of crude oil dropped 6.2% from a year earlier to 7.6 million barrels a day, the lowest imports for August in 18 years.