Oil prices tumbled again on Monday, eroding last week`s gains, as Opec called for co-operation from oil-producing nations outside the cartel.
Brent crude fell 3% to $31.25 a barrel following a 10% surge on Friday, while US oil was $1.02 lower at $31.17.
The slide came as the head of Opec called for all oil-producing nations to work together.
Abdullah al-Badri said both Opec and non-Opec oil producers needed to tackle oversupply to help prices rise.
"It is vital the market addresses the issue of the stock overhang. As you can see from previous cycles, once this overhang starts falling then prices start to rise," he told a conference in London.
Despite the ongoing refusal of Saudi Arabia, the dominant Opec member, to cut production, Mr al-Badri nevertheless blamed countries outside the cartel for the huge global oil glut.
"Yes, Opec provided some of the additional supply last year, but the majority of this has come from non-Opec countries," he said.
Opec accounts for almost 42% of the world`s oil production.
`Future at risk`
The Opec secretary-general said all major producers should agree on methods to reduce stockpiles and thus help prices recover.
"The current environment is putting this future at risk. At current price levels, it is clear that not all of the necessary future investment is viable," Mr al-Badri said.
Prices briefly fell to less than $28 a barrel earlier this month.
The prospect of Opec members cutting production remains unlikely. Indonesia`s Opec representative said that only one member of the cartel supported calling an emergency meeting to discuss ways of boosting oil prices.
The chairman of Saudi Aramco, the state-owned oil giant, said on Monday that prices would ultimately rise to a moderate level as global demand increased.
The Iraqi government said on Monday that oil output reached a record high in December, producing as much as 4.13m barrels a day.
Hans van Cleef, senior energy economist at ABN Amro in Amsterdam, said: "The news that Iraq has probably hit another record builds on the oversupply sentiment. The oversupply will keep markets depressed and prices low."
Iran, which has the world`s fourth-biggest oil reserves, is also preparing to resume exports now that sanctions have been lifted.
- Prada seeks younger customers in bid for growth
- Lotte vice chairman Lee In-won found dead
- German business confidence falls post-Brexit, says Ifo
- Tesla touts speed and driving range with new upgraded battery
- Stocks creep up amid Fed limbo, dollar dips leftright 22leftright 12leftright
- China Crinkles Aluminum Foil Makers
- Cisco to lay off about 14,000 employees: tech news site CRN leftright 22leftright
- UK to avoid recession and world economy to ‘stabilise’ as Brexit shock passes - but US poses biggest risk to global growth
- Fuel prices push up UK inflation rate to 0.6%
- Rio 2016: Kohei Uchimura gets £3,700 Pokemon Go bill