WORLD oil prices ended mixed yesterday as traders weighed disappointing US economic growth data, Europe's debt crisis and the simmering tensions with Iran over its alleged nuclear weapons program.

New York's main contract, West Texas Intermediate crude for delivery in March, slipped 14 cents to US$99.56 a barrel.

In London, Brent North Sea crude for March rose 67 cents to US$111.46 a barrel.

The New York futures contract had opened slightly lower, then turned higher, briefly skimming above US$100, before ending the session nearly flat.

"Looks like we will be range-bound with confecting fears of an uncertain Europe and uncertainty surrounding Iranian oil production," said Phil Flynn at PFG Best.

"Refinery shutdowns and the possibility of an Iranian oil embargo is increasing worries that product supplies may continue to tighten," he added.

Traders digested news that the US economy picked up steam in the fourth quarter but not as much as expected.

The US government estimated the economy, the world's biggest oil consumer, grew at an annual 2.8 percent rate, accelerating from 1.8 percent in the third quarter. Analysts on average forecasted a more robust 3.2 percent pace.

The data came after the US Federal Reserve said Wednesday extended the timeframe for ultra-low interest rates to support the frail recovery.

"The Fed's pledge to keep low interest rates through 2014 and the weaker US dollar should provide some support to commodity markets but global economic growth and demand prospects are not overly encouraging at the moment," BMO Capital Markets analysts said.