U.S. crude settled up $2.22, or 4.5 percent, at $51.43 a barrel on Thursday, its highest settle since March 4 after Saudi Arabia and its Gulf Arab allies began airstrikes in Yemen, sparking fears of a bigger Middle East battle that could disrupt world crude supplies.
The military operation against Houthi rebels, who have driven the president from Yemen's capital Sanaa, has not yet affected oil facilities of major Gulf producers.
But fears the conflict could spread has stoked concerns about the security of Middle East shipments, even as analysts and commentators doubt the probability of an all-out war amid continued signs of crude oversupply.
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Egyptian officials told the Associated Press Egypt and Saudi Arabia would lead a ground incursion into Yemen to root out the Houthis.
Benchmark Brent oil jumped 5 percent early in the session before giving back some of that in European trade as the dollar rebounded from Wednesday's drop, making commodities denominated in the greenback costlier in other currencies.