The OPEC oil cartel on Tuesday raised slightly its world oil demand forecast for 2015, while acknowledging that there remains a supply glut on the market.

In its monthly oil report, the cartel, which pumps out just under a third of the world's crude, raised global oil demand by 60,000 barrels a day for 2015.

The change would only have a marginal impact on the global demand volume, which is expected to reach 92.5 million barrels a day.

Production by non-OPEC countries is meanwhile expected to remain unchanged at 29.32 million barrels a day.

Ministers from the 12-nation cartel are due to meet on June 5.

OPEC has set its production at 30 million barrels a day, refusing to turn down the taps despite an oversupply that has brought prices down.