Oil Prices
The price sign outside Costco in Westminster, Colorado, on Dec. 23, 2014, shows gasoline selling for the lowest price per gallon in years. Prices were down again in Monday trading as Asian markets opened. Reuters

SINGAPORE (Reuters) - Oil prices fell early on Monday after U.S. unions called a refinery strike and traders cashed in on strong price gains last week when the market soared more than 8 percent on a sharp drop in U.S. drilling.

Brent crude oil futures were trading at $51.92 a barrel at 0100 GMT and U.S. WTI futures were at $47.17 a barrel, both down $1.07 a barrel.

The drops followed a jump back from six-year lows on Friday, as a record weekly decline in U.S. oil drilling fueled a frenzy of short-covering.

Asian oil markets also opened to news of a strike at U.S. refineries and chemical plants, potentially denting crude demand in coming days.

The United Steelworkers union called strikes at nine U.S. refineries on Sunday to bring about a new national agreement that covers workers at 63 refineries, accounting for two-thirds of U.S. refining capacity, said a source familiar with the union's plans.

Despite Monday's price falls, the jump late last week means that oil prices ended a run of range-bound trading following earlier steep falls.

International Brent benchmarks rose back above $50 per barrel for the first since early January, and they also jumped above its 15 exponential daily moving average (DMA) value, a key technical indicator, for the first time this year.

Analysts said that Monday's falls were driven by technical factors.

Brent oil may break support at $51.72 per barrel and fall to $50.93, as indicated by its wave pattern and a Fibonacci projection analysis, said Reuters market analyst Wang Tao.

A sharp gain on Jan. 30 was driven by a wave C, the third wave of a three-wave cycle that developed from the Jan. 13 low of $45.19. The Fibonacci projection analysis on the target of this wave reveals it may have peaked around key resistance at $53, the 100-percent level, he added.