Production by the Organization of the Petroleum Exporting Countries fell by over a half million barrels a day last month to 29.6 million bpd, the Wall Street Journal reported.
Iraq’s output fell about 300,000 barrels a day to lead the overall decline.
Angola, Libya, and Saudi Arabia also reported drops in production last month.
OPEC supplies about a third of the oil consumed globally each day.
Iraq’s pullback to 3.2 million barrels a day comes after the country’s February production hit a 35-year peak, the Wall Street Journal said.
“Infrastructure constraints have slowed the development of several oil fields and led many analysts to question whether February’s surge in output was sustainable,” the paper said.
Angola’s oil production fell by 150,000 bpd in March.
Libya’s production declined by 118,000 barrels a day because of rebel blockades of key ports.
Saudi Arabia, OPEC’s biggest producer, reduced crude output by 81,000 barrels a day to 9.7 million bpd in March.