U.S. West Texas Intermediate crude oil futures dropped 75 cents to $45.79 a barrel by 0900 GMT.
International Brent crude futures were down 50 cents at $54.41 a barrel.
In physical oil markets, top exporter Saudi Arabia is expected to cut February prices for heavier crude grades sold to Asia by up to 50 cents a barrel due to weaker fuel oil margins, respondents to a Reuters survey said on Thursday.
“Fears of future economic and earnings growth continue to be the main driver in causing market jitters,” Singapore-based brokerage Phillip Futures said.
Markets were roiled by a more than 3 percent slump in the U.S. dollar against the Japanese yen, and after tech giant Apple cut its sales forecast.
“We did not foresee the magnitude of the economic deceleration, particularly in Greater China,” Apple chief executive Tim Cook said.
The slowdown in China and turmoil in stock and currency markets appears to be making investors nervous, including in oil markets.
“This is a continuation of the volatility afflicting commodities and oil with the last 24 hours marked by the release of various weak economic data points, particularly manufacturing PMIs, for major economies,” consultancy JBC Energy said.
Oil markets are also under pressure from a surge in supply just as demand growth is expected to slow.
U.S. crude production stood at a record 11.7 million barrels per day (bpd) in late 2018, making America the world’s biggest oil producer.
Speaking to reporters on Wednesday, U.S. President Donald Trump said U.S. pressure had kept production high among allies in the Organization of the Petroleum Exporting Countries.
“People see that gasoline is way down and the reason it’s way down is because I called up some of the OPEC people,” Trump said. “I made calls, I said you better let that oil, that gasoline flow, and they did,” he added.
Others are not sitting idle, with Russian output reaching a record of more than 11 million bpd in 2018.
Supply from Iraq, the second-biggest producer in OPEC, is also up, with December exports at 3.73 million bpd versus 3.37 million bpd in November.
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