U.S. light crude climbed 23 cents to $50.60 a barrel, about 13 percent below the all-time record $58.28 struck on April 4 but still 16 percent above prices at the end of 2004.London's Brent crude rose 22 cents to $51.00 a barrel. "More and more people are becoming convinced that oil above $55 is not sustainable in the long term. But a lot of people are willing to come back into the market when prices go below $50," said David Thurtell, a Sydney-based commodities strategist at Commonwealth Bank of Australia. "If U.S. stocks continue to build we could come down to the $46 mark." The head of OPEC said on Monday the producers' cartel, which controls 40 percent of global exports, would increase supplies to near 25-year highs next month although it would postpone a formal rise to official output limits until a June meeting. President Sheikh Ahmad al-Fahd al-Sabah, also Kuwait's energy minister, said OPEC output would add 500,000 barrels per day (bpd) to output in May to prepare for a surge in demand later in the year ahead of the northern hemisphere winter. Top exporter Saudi Arabia has already told customers to expect more oil in May.