Oil prices rallied for a third straight session on Wednesday, as the Organization of the Petroleum Exporting Countries (OPEC) said the oil market showed signs of rebalancing.

World oil demand growth in 2017 is now expected to increase by 1.5 million barrels per day, representing an upward revision from previous report, mainly reflecting recent data showing an improvement in economic activities, according to the OPEC's monthly report on Wednesday.

In 2018, world oil demand is anticipated to grow by 1.4 million barrels per day, due to the improving economic outlook in the world economy, particularly China and Russia, the report added.

The OPEC also said the oil market was gradually tightening after years of supply glut.

The West Texas Intermediate for November delivery increased 0.38 U.S. dollar to settle at 51.30 dollars a barrel on the New York Mercantile Exchange, while Brent crude for December delivery rose 0.33 dollar to close at 56.94 dollars a barrel on the London ICE Futures Exchange.