Oil prices rose for the third day in a row Friday as traders brushed aside rising crude inventories and signs of slowing demand growth and focused instead on fears that producers will have trouble keeping the market adequately supplied longer term.

Light sweet crude (search) for June delivery rose 22 cents to $51.05 a barrel in afternoon trading on the New York Mercantile Exchange (search). Earlier in the week, oil prices traded below $50 a barrel.

Brent crude futures rose 54 cents on the International Petroleum Exchange (search), fetching $51.67 a barrel.

Nymex gasoline futures rose more than 1 cent to $1.49 a gallon. Heating oil futures fell less than a penny to $1.44 a gallon.

The U.S. Energy Department's latest petroleum supply report, released Wednesday, showed that gasoline demand over the past month has grown by less than 1 percent, compared with a year ago, a rate of growth that some analysts believe reflects motorists' sensitivity to high prices. The average retail price of gasoline in the U.S. is $2.24 a gallon, or roughly 40 cents higher than a year ago.

Some analysts believe the drop in demand growth will prove temporary.

Kevin Norrish, the head of commodities research at Barclays Capital in London, said that over the next few weeks U.S. gasoline prices "are going to fall, which means we're going to see increased demand."

Beyond the U.S. market, there are concerns about whether the largest oil producing countries will be able to keep up with rising worldwide demand.

In Hong Kong, Morgan Stanley economist Andy Xie said traders were "very concerned" that the Organization of Petroleum Exporting Countries (search), whose member countries produce 40 percent of the world's oil, may not be able to meet the anticipated surge in demand later this year. Average global demand is expected to exceed 84 million barrels a day in 2005, with daily demand in the fourth quarter reaching 87 million barrels a day or more.

Crude futures are around 30 percent above year-ago levels but would need to surpass $90 a barrel to exceed the inflation-adjusted high set in 1980.