Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Oil prices fell slightly on Thursday amid volatile currency and stock markets, coupled with concerns that an economic slowdown in 2019 will curb fuel demand just as crude supplies are surging.

Markets were buffeted by a 4.4 percent slump in the U.S. dollar and after tech giant Apple cut its sales forecast for the first time in nearly 12 years.

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 for major economies," said consultancy JBC Energy.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

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.

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 in late 2018, making America the world's biggest oil producer.

Speaking to reporters on Wednesday, 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," Trump 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.