LONDON—U.S. oil fell on Monday after airlines called off thousands of flights over the Christmas holidays amid surging COVID-19 cases, though Brent crude gained support from hopes that the Omicron variant will have a limited impact on global demand. More than 1,300 flights were canceled by U.S. airlines on Sunday as COVID-19 reduced the number of available crews while several cruise ships had to cancel stops. U.S. West Texas Intermediate (WTI) crude was down 89 cents, or 1.2 percent, at $72.90 a barrel by 0948 GMT. The U.S. market was closed on Friday for a holiday. Global benchmark Brent crude rose 12 cents, or 0.2 percent, to $76.26. “Lower travel equalling lower economic activity in the U.S. equals lower WTI,” said Jeffrey Halley, analyst at brokerage OANDA, who added that the divergence between Brent and WTI could reflect that recovery remains on course. “The disruption to goods and services from …