U.S. imports of crude oil in August were the lowest they've been in almost 20 years, the American Petroleum Institute said.

API said in its monthly report on trends in the U.S. energy sector crude oil imports of 7.6 million barrels per day in August, the last full month for which data are available, was 6.2 percent less than last year and the lowest level for August since 1996.

Total imports of petroleum productions were down 10.2 percent year-on-year.

August crude oil production of 8.6 million bpd, meanwhile, was the highest for the month in nearly three decades. Production was boosted largely by output from North Dakota and Texas.

In terms of demand, API said its petroleum delivery metric showed a 1 percent increase year-on-year to 19.3 million bpd, the highest in three years.

"Petroleum demand last month showed slow but steady growth, mirroring economic indicators for domestic manufacturing, air travel and job creation," said API Chief Economist John Felmy.

Production of gasoline in August was 4.6 percent higher year-on-year, while demand fell to its lowest level for August since 2011.

Gasoline prices since August have declined as the summer vacation season waned.