International benchmark Brent crude futures were down 30 cents at $71.98 per barrel by 2:24 p.m. ET. U.S. West Texas Intermediate crude futures fell 13 cents to $66.81 a barrel, ending Thursday's session at a fresh seven-week low.
Both benchmarks tumbled more than 3 percent on Wednesday after U.S. data showed a smaller-than-expected weekly draw in crude inventories and a surprise build of 2.9 million barrels in gasoline supplies. Analysts polled by Reuters had forecast a 1.7 million-barrel draw in gasoline stocks.
"The ability of gasoline to hang in there despite strong demand weighed on the market," said John Kilduff, a partner at Again Capital Management in New York. Previously the market had been "racing higher" due to a fear of scarcity, but those concerns have receded, he said. "Supply is seen as sufficient to meet the pretty robust demand picture."
The ongoing trade war is rattling global markets and investors fear any slowdown in the world's two largest economies would slash demand for commodities.
On top of the impact on the broader global economy, there is growing worry in the crude oil market about Chinese demand. Crude imports picked up in July after two months of decline, but were still among the lowest this year due to a drop-off in demand from smaller independent refineries.
In another sign that exporters are preparing for slower demand from some of the big Asian buyers, Iraq cut its official selling price for September cargoes of Basra Light crude for its Asian customers on Thursday.
The United States on Tuesday reimposed sanctions on Iran, the third-biggest producer in the Organization of the Petroleum Exporting Countries.
"The geopolitical risk from Iran is keeping a floor under the price," he said.
The renewed sanctions will not directly target Iranian oil until November, although U.S. President Donald Trump has said he wants as many countries as possible to cut their imports of Iranian crude to zero.
"The impact of it is the greatest known unknown of the year. If worst comes to worst and 1.5-2 million bpd of Iranian disappears from the market ... calculations will go out of the window and oil bears will have to brace themselves for a very rough ride," PVM Oil Associates analyst Tamas Varga said.
— CNBC's Tom DiChristopher contributed to this report.