OPEC production climbed by the most in almost four years as Saudi Arabia, Iraq and Libya boosted output amid a stronger outlook for global oil demand, according to the International Energy Agency. The Organization of Petroleum Exporting Countries raised output by 890,000 barrels a day to 31.02 million a day in March, the biggest monthly gain since June 2011, the IEA estimated. Oil prices are 45 percent lower than a year ago, trading at $59 a barrel in London today, as OPEC maintains a policy of defending market share in response to booming U.S. shale output.