Oil prices rose Monday as a gas leak closed a large Norwegian North Sea oil field and the threat of a colder-than-normal U.S. winter fueled worries about low heating oil stocks.

North Sea Brent blend jumped $1.18 a barrel to $45.75 and U.S. crude was up 32 cents at $49.76 after a four-day holiday break.

Prices rose as a gas leak forced closure of the 130,000-barrel-per-day Snorre A platform and the 75,000 bpd Vigdis field in the Norwegian North Sea.

Rising world demand has left little spare capacity in the world supply system, magnifying the impact of sudden disruptions. In Canada, the 165,000-bpd Terra Nova platform has been shut for the past week for the investigation of an oil spill.

Crude is up 50 percent for the year and holding strong because of concerns that lean heating fuel stocks would leave the Northern Hemisphere ill-prepared to deal with a severe winter.

"The heating oil market is ... highly vulnerable to a sudden cold spell," Deutsche Bank said in a weekly report.

"Underlying strength in the energy complex has been driven by a ... draw in (U.S.) heating oil at a time when reduced weather-driven demand in North America suggests that stocks should be building," the report added.

The U.S. government last week reported that distillate stocks -- including diesel and heating oil -- had risen for the first week in 10, but that heating oil inventories were 16 percent below last year.

Analysts expected this week's inventory report to show distillates up another 1.3 million barrels, as mild weather in the Northeast caps demand.

While winter weather in the heavy-consuming U.S. Northeast has so far been relatively warm, many forecasters are predicting a colder-than-usual season in the months ahead.

Saudi Oil Minister Ali al-Naimi said Monday that while global stocks of petroleum products, including heating oil, remained below par, stocks were gradually rebuilding in consuming countries.

"The (crude) supply is a little bit ahead of demand. Inventories are building comfortably. I recognize some of the products such as heating oil are not at the right level, but as refineries come back from turnaround the market will be better balanced," he said.

OPEC (news - web sites) producers are enjoying less of a windfall than $50 oil prices suggest, as big discounts for their lower-quality crude and a weak dollar hit export earnings, OPEC officials said on Monday.

The double drain on revenues has convinced OPEC's second biggest producer, Iran, that the group should mop up some 900,000 bpd of leakage above formal supply limits of 27 million. OPEC ministers meet on Dec. 10 in Cairo.

"I would say we in OPEC have to go back to our quota first, because the market has 2 million bpd oversupply," Iran OPEC Governor Hossein Kazempour Ardebili told Reuters in a written response to questions.

Heavy falls in the dollar have also sliced into OPEC members' purchasing power for goods and services from non-dollar economies, like the eurozone.

"I'm very concerned about the weak dollar and that will reflect on oil producers' decisions," Qatari Energy Minister Abdullah al-Attiyah told Reuters.

  OPEC has previously cited the U.S. currency's weakness against other major currencies as justification for acting to keep dollar-denominated world oil prices high.