Investing.com - Crude prices mostly higher on Tuesday, although West Texas Intermediate struggled around the unchanged mark, as investors looked ahead to weekly data from the U.S. on stockpiles of crude and refined products to gauge the strength of demand in the world’s largest energy consumer.

Industry group the American Petroleum Institute is due to release its weekly report at 4:30PM ET (20:30GMT) Tuesday. Official data from the Energy Information Administration will be released Wednesday, amid forecasts for an oil-stock gain of around 0.4 million barrels.

U.S. West Texas Intermediate (WTI) crude futures inched up 1 cent, or 0.02%, to $65.56 a barrel by 10:27AM ET (14:27GMT).

Meanwhile, Brent crude futures, the benchmark for oil prices outside the U.S., added 29 cents, or roughly 0.4%, to $69.81 a barrel.

Oil prices ended slightly lower on Monday, as rising drilling activity in the United States pointed to further increases in shale output, underlining concerns about a return of oversupply.

The U.S. rig count, an early indicator of future output, is much higher than a year ago as energy companies have continued to boost spending since mid-2016 when crude prices began recovering from a two-year crash.

U.S. oil production, driven by shale extraction, rose to an all-time high of 10.40 million barrels per day (bpd) last week, staying above Saudi Arabia's output levels and within reach of Russia, the world's biggest crude producer.

Analysts and traders have recently warned that booming U.S. shale oil production could potentially derail OPEC's effort to end a supply glut.

OPEC, along with some non-OPEC members led by Russia, have been restraining production by 1.8 million barrels per day (bpd) to curb the market of excess supply. The arrangement, which was adopted last winter, expires at the end of 2018.

Talk of a possible extension of the deal, coupled with concern of supply disruptions from tensions in the Middle East, have buoyed oil prices in March. The U.S. benchmark is on track for monthly gains of 6.2%, while the London barrel is up around 5.9% so far this month.

Saudi Energy Minister Khalid al-Falih said last week that OPEC members would need to continue coordinating with Russia and other non-OPEC oil-producing countries on supply curbs in 2019 to reduce global oil inventories.

Some analysts have warned that such an agreement could actually be harmful as current, or higher, prices could entice even more U.S. shale producers to increase output.

In other energy trading, gasoline futures tacked on 0.4% to $2.0255 a gallon, while heating oil gained 0.6% to $2.0297 a gallon.

Natural gas futures jumped 1.7 cents, or 0.6%, to $2.674 per million British thermal units.