Associated Press - November 19, 2009 4:14 PM ET

CHEYENNE, Wyo. (AP) - The roof of a storage tank containing crude oil at a Sinclair Oil refinery collapsed in 2007, more than two years before it happened again at the refinery and caused Wyoming's biggest spill in decades.

Leaks in the pontoons holding up the floating roofs are the suspected cause both times.

The May 3 spill of nearly 3 million gallons of gasoline-grade fluid created a serious explosion risk next to the town of Sinclair.

The Wyoming Department of Environmental Quality learned about the Jan. 20, 2007, roof collapse during an inspection that November. The Associated Press learned about the incident through a records request.

Salt Lake City-based Sinclair did not immediately return a message Thursday seeking comment.

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