By Florence Tan

SINGAPORE (Reuters) - Oil prices were mixed on Monday, with Brent edging up while U.S. crude futures slipped after airlines called off thousands of flights in the United States over Christmas holidays amid surging COVID-19 infections.

U.S. West Texas Intermediate crude futures fell 41 cents, or 0.6%, to $73.38 a barrel by 0053 GMT. The contract did not trade on Friday because U.S. markets were closed for the Christmas holiday.

Brent crude rose 40 cents, or 0.5%, to $76.54 a barrel after settling down 0.92% on Friday.

Both contracts jumped 3% to 4% last week after early data suggested that the Omicron variant of COVID-19 may cause a milder level of illness.

However, the highly transmissible variant is causing COVID-19 case numbers to surge across the world.

In the past three days, thousands of passengers travelling during Christmas have been stranded after U.S. airlines cancelled flights due to COVID-related staffing shortages.

In Europe, natural gas prices touched record highs last week on tight supplies, supporting Brent crude prices.

Russian President Vladimir Putin said on Friday that the European Union can only blame its own policies for record gas prices, saying some of its members resell cheap Russian gas at much higher prices within the bloc.

Looking ahead, oil investors are focused on the next OPEC+ meeting on Jan. 4.

The Organization of the Petroleum Exporting Countries (OPEC and allies including Russia, known as OPEC+, will meet to decide whether to go ahead with a 400,000 barrels per day (bpd) production increase in February.

Russia believes oil prices are unlikely to change significantly next year with demand recovering to pre-pandemic levels only by the end of 2022, Deputy Prime Minister Alexander Novak said on Friday.