Investing.com - Crude prices were slightly lower in early dealings on Thursday, amid speculation weekly supply data due later in the day will show a sizable gain in U.S. gasoline and fuel supplies.

The U.S. Energy Information Administration will release its official weekly oil supplies report for the week ended Jan. 12 at 11:00AM ET (1600GMT) Thursday. The report comes out one day later than usual due to the Martin Luther King Day holiday.

After markets closed Wednesday, the American Petroleum Institute said that U.S. oil inventories dropped by nearly 5.1 million barrels last week. That compared with analysts' expectations for a decline of around 3.6 million barrels.

However, the API report also showed a gain of 1.8 million barrels in gasoline stocks, while distillate stocks, which include motor diesel and heating oil, increased by about 609,000 barrels.

There are often sharp divergences between the API estimates and the official figures from EIA.

U.S. West Texas Intermediate (WTI) crude futures shed 5 cents to $63.91 a barrel by 3:30AM ET (0830GMT). It rose to its highest since Dec. 2014 at $64.89 on Monday.

Meanwhile, Brent crude futures, the benchmark for oil prices outside the U.S., were at $69.22 a barrel, down 16 cents from their last close. The contract reached $70.37 on Monday, its best level since Dec. 2014.

Oil futures settled with modest gains Wednesday, as WTI ended 0.4% higher and Brent added 0.3%.

Prices have increased around 13% since early December, benefiting from production cut efforts led by the Organization of the Petroleum Exporting Countries and Russia. The producers agreed in December to extend current oil output cuts until the end of 2018.

The deal to cut oil output by 1.8 million barrels a day (bpd) was adopted last winter by OPEC, Russia and nine other global producers. The agreement was due to end in March 2018, having already been extended once.

Analysts and traders have recently warned that U.S. shale oil producers could ramp up production in the coming weeks as they look to take advantage of higher prices, potentially derailing an OPEC-led effort to curb excess supply.

Oil traders are also looking ahead to a monthly report from the Organization of Petroleum Exporting Counties due later in the session to assess global oil supply and demand levels. The data will give traders a better picture of whether a global rebalancing is taking place in the oil market.

In other energy trading, gasoline futures dipped 0.2% to $1.864 a gallon, while heating oil was down 0.2% at $2.065 a gallon.

Natural gas futures slipped 1.5 cents to $3.218 per million British thermal units, as traders looked ahead to weekly storage data due later in the global day.