Oil prices fell on Monday as worries about oversupply in North America and a strong dollar pushed Brent futures towards $59 a barrel and U.S. contracts below $49 a barrel.

Oil prices edged up after early falls on Monday as parts of Asia returned from the Lunar New Year holiday, with Brent futures moving further away from $60 a barrel and U.S. contracts moving towards $51.

The U.S. refinery strike widened as workers at the nation's largest refinery walked off their jobs at 12 a.m. CST (0600 GMT) on Saturday, according to the United Steelworkers union (USW).

Lead U.S. oil company negotiator Shell Oil Co said face-to-face negotiations on Friday with the United Steelworkers union (USW) failed to yield an agreement to end the 20-day-old U.S. refinery strike.

Crude prices ended mixed on Friday as the number of U.S. rigs drilling for oil fell far less than expected this week, while heating oil jumped 6 percent after severe winter cold crimped output at three refineries.

Brent crude oil fell below $60 a barrel on Friday as oversupply, supported by record-high U.S. crude stocks, weighed on the market.

Oil markets edged up on Friday to halt a two-day drop, helped by expectations that data later in the day would show a continuing decline in the U.S. oil rig count, a clear sign of the pressure the tumble in crude has put on oil producers.

Oil prices tumbled on Thursday as U.S. inventories were expected to hit record highs, while a possible rise in Saudi output could stoke oversupply built up in the past few months.

An explosion and fire ripped through a gasoline processing unit at an Exxon Mobil Corp refinery near Los Angeles on Wednesday, leaving California with the threat of higher gasoline prices.

Oil dropped below $62 a barrel on Wednesday, failing to build on gains of more than 1 percent in the previous session as analysts said a recent rally in prices was overblown.