API said, in its latest survey, that U.S. petroleum deliveries for August were up 2.8 percent compared to the previous month but down 4.3 percent when compared to the same time last year.
U.S. petroleum deliveries for August were 18.6 million barrels per day, the lowest level for the month in 15 years, the industry group said.
For gasoline, demand was down nearly 1 percent in August compared to 2011 figures for the same month. Though API didn't speculate on the demand specifics, retail gasoline prices in August peaked around $4 per gallon in some markets because of Hurricane Isaac.
AP Chief Economist John Felmy said contraction in the U.S. manufacturing sector may be contributing to lower demand for petroleum products.
"Given the nation's weak employment situation, it's no surprise petroleum demand was off," he added.
The U.S. Labor Department reported August unemployment was 8.1 percent. Unemployment figures for September are expected Oct. 5.
Crude oil imports declined modestly as did oil production, which API said was largely the result of the late August hurricane.