Tuesday as Saudi Arabia's oil minister would not be drawn on the outcome of OPEC's upcoming meeting on crude production levels.

"We will discuss... and then decide" on output, Saudi Arabia's oil minister Ali al-Naimi told reporters on arrival in Vienna ahead of Friday's meeting of the Organization of the Petroleum Exporting Countries in the Austrian capital.

The cartel is widely expected to maintain high output levels despite a global supply glut, with OPEC kingpin Saudi keen to hold onto market share in the face of strong competition from US shale oil production.

Around 1745 GMT, US benchmark West Texas Intermediate for delivery in January stood at $41.51 a barrel, down 14 cents from the close on Monday.

Brent North Sea crude for January fell 19 cents to $44.42 a barrel.

"Crude prices are likely to stay sideways ahead of the OPEC meeting, where Iran is expected to announce plans to expand output," said Bernard Aw, market strategist at IG Markets in Singapore.

Iran, one of a dozen OPEC members, is expected to increase its oil exports after crippling Western sanctions are lifted under a deal reached with major world powers in July to curb its nuclear programme.

The sanctions have restricted Iranian oil shipments and analysts say their return to the market will further add to the crude oversupply.

Iran's deputy foreign minister Abbas Araghchi said last week his country expects the deal to come into force in early January, when Tehran will have implemented its commitments.

Oil prices have been in retreat from levels above $100 a barrel reached in mid-2014.

Prices were unchanged Tuesday also after a key measure of China's manufacturing activity dropped to its weakest level in more than three years in November, further underlining weaknesses in the world's top energy consumer, traders said.