The start was held-up as the ministers met informally late into the evening, to try to reach a common position on boosting prices, which are at their lowest for 12 years.

The oil price is about 40% down on last year and many forecasts say it has further to go - big non-Opec producers like Mexico and Russia are thought to be reluctant to cut output, a measure that some Opec members have been pushing for.

The BBC business correspondent, Mark Fisher, says Opec countries are in disarray on what to do about oil prices - they seem to agree on little except that they're far too low with the average price per barrel slumping to $12.33 in the third quarter of this year, compared with $18.03 at the same time last year.

He says the formal session is expected to focus on accusations that some Opec members, including Venezuela and Iran, have not honoured an agreement made earlier this year for cuts in production.

Internal divisions

Will member countries be able to agree new measures?

Production cuts agreed at a meeting in June were designed to boost flagging prices.

But some member countries are seen as not complying fully with the agreement and there are likely to be calls at the meeting for them to do so.

Venezuela stands accused of increasing output for domestic political reasons ahead of December presidential elections.

There are also growing concerns that Iran is wavering on its promise to reduce supplies as it has said it was asked to cut from too low a baseline.

Opec produces around 26.9m barrels of oil a day.

New moves unlikely

The chance of any new action to tackle the problem looks negligible.

Saudi Arabia, OPEC's leading policy maker, has ruled out more output curbs, insisting it wants full adherence to existing limits.

Riyadh is concerned that it should not be left to shoulder the burden of supply restraint leaving rivals to grab market share - a situation it vowed never to repeat after the last big oil slump in 1986.

Ministers are expected to consider only prolonging current measures by six months to the end of next year.

This will provide little comfort to a market where Brent crude was valued at $11.24 a barrel on Wednesday, near historical lows and the lowest it has been valued since 1976.