NEW YORK, July 5 (Reuters) - Office staff returned to work at the Coffeyville Resources refinery in Coffeyville, Kansas, which was shut by severe flooding earlier this week, the company said in a press release.

Part of the 108,000 barrel-per-day refinery remained under water. Workers will wait until the floodwaters subside before making damage assessments and determining when the refinery can restart.

The flooding also led to an oil spill after the refinery's main crude oil tank overflowed. The overflow was halted, but an updated estimate of the amount of oil spilled was available. Preliminary assessments put the amount of oil spilled at 1,000 barrels.

Oil traders have speculated the Coffeyville facility, which sources much of its crude oil from the NYMEX delivery point at Cushing, Oklahoma, could be shut for some time because the flooding probably damaged pumps and electrical equipment.

Refinery outages in the Cushing region have contributed to pushing WTI crude futures to a discount to North Sea Brent since February.

Refineries on the U.S. Gulf Coast damaged by floods caused by Hurricane Katrina in 2005 were shut for months although these restarts were complicated by extensive damage to regional electricity infrastructure as well as to workers' homes.

Coffeyville Resources LLC is owned by CVR Energy Inc., a private company controlled by Goldman Sachs and the Kelso funds. CVR had been expected to sell shares in an initial public offering later this year on the New York Stock Exchange.

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