Brent crude oil prices started Tuesday's Asian trading under $80 a barrel as traders lowered their expectation of a significant output cut by oil producers' club Opec.

Oil ministers from the Organization of Petroleum Exporting Countries (Opec) meet on Thursday in Vienna and some are imploring the group to cut 1 million barrels per day or more to support prices that have fallen about 30 percent since June on the back of rising supply being met by cooling demand.

Non-member Russia, which needs higher prices to support its economy, tried to sway Opec to slash production, suggesting Moscow could cut its own crude output by about 300,000 barrels a day, yet analysts said its efforts may be in vain.

"Investors appear to have lowered the probability of a production cut at this week's Opec summit," ANZ bank said in a morning note on Tuesday.

Brent was trading at $79.43 a barrel at 0140 GMT, down 25 cents. US crude was down 11 cents to $75.67 a barrel.

Libya, Venezuela, Iran and Ecuador have called for Opec and its 12 member states to cut production, while Kuwait has said an output reduction is unlikely.

Key will be what the club's biggest producer and exporter Saudi Arabia decides, with some analysts expecting no price supporting action from the kingdom.

"The rapid growth now being achieved in non-Opec production means it faces the risk that even a large cut to supply may not be enough to support prices and could simply result in lost market share and revenue," Barclays Bank said.

"Saudi Arabia's response so far to falling oil prices is an acknowledgment that it is less able to influence oil prices than at any time over the past decade," it added.

Some commodity fund managers believe oil prices could slide to $60 per barrel if Opec does not agree a significant output cut. – Reuters