Oil prices fell on Monday on the potential return of output from Libya as rising coronavirus cases also added to worries about global demand, although a tropical storm heading for the U.S. Gulf of Mexico limited losses.

Brent crude was down 33 cents, or 0.8%, at $42.82 a barrel by 0645 GMT, while U.S. crude was down 38 cents, or 0.9%, to $40.73 a barrel.

Workers at Libya’s major Sharara field have restarted operations, two engineers working there said, after National Oil Corporation announced a partial lifting of force majeure. But it was still unclear when production might restart.

“The market can ill afford more crude hitting the market,” ANZ analysts said in a note on Monday, at a time when coronavirus-related curbs have eroded demand.