NEW YORK, Dec. 112 (Xinhua) -- Oil prices fell on Wednesday, as global oil demand growth is expected to slow next year, OPEC said in its monthly report in December.

Global oil demand is forecast to increase by around 1.29 million barrels per day (bpd) to average 100.1 million bpd, lower than the initial forecast in July, said the Wednesday report.

Based on the above forecasts, demand for OPEC crude in 2019 is expected to stand at 31.4 million bpd, which is lower than the demand levels seen this year, according to the report.

Looking ahead, the report noted that the upside for crude appeared "limited," because "rising trade tensions, monetary tightening and geopolitical challenges are among the issues that skew economic risks even further to the downside in 2019."

The oil producing group continued to point out that upside risks relate to the development of the overall economy and the price environment, while downside risks concern the economy, fuel substitution, vehicle efficiency and the high baseline seen in oil demand during the last four years.

The West Texas Intermediate for January delivery decreased 0.5 U.S. dollar to settle at 51.15 dollars a barrel on the New York Mercantile Exchange, while Brent crude for January delivery decreased 0.05 dollar to close at 60.15 dollars a barrel on the London ICE Futures Exchange.