London - Brent crude oil fell more than $2 a barrel on Monday to a new five-year low on predictions that oversupply would keep building until next year after Opec decided not to cut output.
In a report dated 5 December, Morgan Stanley said oil prices could fall as low as $43 a barrel next year.
The US investment bank cut its average 2015 Brent base-case outlook by $28 to $70 per barrel and by $14 to $88 a barrel for 2016.
"Without Opec intervention, markets risk becoming unbalanced, with peak oversupply likely in the second quarter of 2015," Morgan Stanley analyst Adam Longson said.
Brent for January was down $1.77 at $67.30 a barrel after lunch, having fallen $2.30 to $66.77 - its lowest since October 2009.
US crude was down $1.44 at $64.40 a barrel, after hitting a session low of $64.14. The US contract, also known as West Texas Intermediate, touched $63.72 last week, its lowest since July 2009.
Driving further slide
Top oil exporter Saudi Arabia at a meeting last month resisted calls from poorer members of the Organisation of the Petroleum Exporting Countries to cut production, driving a further slide in prices, which have lost more than 40% since June.
Cartel member Kuwait said on Monday oil prices were likely to remain around $65 a barrel for the next six to seven months.
"I think oil prices will remain at these levels ... until world economic recovery is clear or if there were any political crises or Opec changed its production policy," said Nizar al-Adsani, chief executive of Kuwait's state oil company.
Libyan state oil company NOC said on Sunday the country was producing 800 000 barrels per day, though its El Sharara oilfield was closed due to a pipeline blockade.