Oil prices fell on Wednesday as ample supply pressured futures even as the prospect of economic stimulus from China boosted equities markets.
U.S. shares seesawed after a stronger open, a more muted reaction after Europe's equities were buoyed by an 8 percent jump in Japanese stocks and the prospect of more stimulus from China.
Oil prices remained in retreat on concerns about swollen inventories, high global production and the increasing likelihood that Iranian barrels will return to export markets even as slowing growth in China threatens demand.
"The failure of oil markets to move higher on the back of this macroeconomic optimism calls fresh attention to the oil market's weak direct physical fundamentals," Tim Evans, energy futures specialist at Citi Futures, said in note.
Brent crude was down 88 cents at $48.64 a barrel at 12:19 p.m. EDT (1619 GMT), after climbing 4 percent in the previous session.
U.S. crude was off 67 cents at $45.27, having eased on Tuesday as trading resumed after the Monday's Labor Day holiday.
The U.S. summer driving season is ending. Gasoline demand in the United States has been supportive for oil prices at a time when the global demand picture is clouded by worries about China's economy.
The U.S. Energy Information Administration (EIA) cut its forecast for 2015 and 2016 world oil demand growth in its monthly report.
Traders awaited a fresh snapshot of U.S. oil inventories from industry and government, starting with American Petroleum Institute (API) data due at 4:30 p.m. EDT.
Analysts surveyed by Reuters on Tuesday expected crude stocks to be up slightly.
While Saudi Arabia's crude oil production dipped by 100,000 barrels per day (bpd) in August, the Organization of the Petroleum Exporting Countries continued to produce close to record volumes.
Russia and Mexico have indicated they will not cut production, cooling speculation that some producers might organize to lower output to support prices.
Britain's oil and gas industry association said the country's output is set to post a gain in 2015, the first in 15 years, reflecting investment in more efficient technology.
Oil prices are off more than 50 percent since June 2014 because of the global supply glut. In recent weeks, oil fell to 6-1/2-year lows before rallying in volatile trading after a stock market slide in China sent global equities and commodities prices tumbling.