U.S. West Texas Intermediate (WTI) crude futures were down 37 cents, or 0.5 percent, at $73.77 per barrel.
While Saudi Arabia is facing mounting pressure from Trump to do more, America's oil sanctions on Iran and trade frictions with China are adding to uncertainties with planned U.S. tariffs on Chinese goods set to start tomorow.
OPEC and Russian Federation announced in June they were willing to raise output to address concerns of emerging supply shortages due to unplanned disruptions from Venezuela to Libya, and likely also to replace a potential fall in Iranian supplies due to United States sanctions.
Saudi Arabia's total supplies to the market in June were even higher than well-head production, the sources said, suggesting the Kingdom sold crude from storage.
Saudi Arabia had political reasons to respond positively to Trump's request, given its animosity to arch-rival Iran, which Trump is trying to bring to its knees through strict new sanctions. Data from the Energy Information Administration is due Thursday, published a day later than normal because of the Independence Day break.
In response, Iranian oil official Hossein Kazempour Ardebili said that Trump should stop tweeting because his statements have pushed oil prices up by about US$10 a barrel, according to Oil Ministry news service, Shana.
"The OPEC Monopoly must remember that gas prices are up & they are doing little to help".
"This must be a two way street", he wrote, adding in block capitals, "REDUCE PRICING NOW!" Global benchmark Brent LCOc1 was down 39 cents at $77 a barrel.
Meanwhile, China's commerce ministry said on Thursday the United States is "opening fire on the entire world", warning that Washington's proposed tariffs on Chinese goods will hit worldwide supply chains.
South Korea halted all Iranian oil shipments in July for the first time in six years amid USA pressure.
After all the tough talk by the U.S. about countries cutting oil purchases from Iran to zero by November 4, India will have a chance to discuss the issue of crucial energy imports when a team of officials from the state and treasury departments visits the country this month.
US tariffs on $34 billion in Chinese imports took effect as a deadline passed on Friday and Beijing has vowed to respond in kind.