Oil oil rig flanges gulf coast production dropped to 1.293 million barrels per day in May, the lowest level since Sept. 2012, and was 20 percent below the levels seen the same month a year ago.

Natural gas output from Western Europe's top supplier came in at 308.4 million cubic metres (mcm) per day, also below the forecast, but 5 percent higher from a year ago.

"The main reason for the oil production's fall was maintenance at many fields combined with some technical problems," an NPD official said.

"May is normally a maintenance season," he added.

Maintenance affected oil rig flanges gulf coast production at offshore fields operated by Equinor, formerly known as Statoil, including Norway's largest oil and gas field, Troll.

(Reporting by Nerijus Adomaitis, editing by Terje Solsvik)