Workers Tuesday were trying to contain an oil spill that dumped 21,000 gallons into the Gulf of Mexico after a pipeline ruptured.

The U.S. Coast Guard said the spill, about 30 miles southeast of Galveston, Texas, came from a rupture in a medium crude oil pipeline owned by Houston-based Plains All American Pipeline.

The company detected a pressure loss in the High Island Pipeline System and shut the line down early Sunday, Coast Guard Petty Officer Mario Romero said. The company was trying to contain the spill Tuesday and suctioning oil from the line.

The spill was not disrupting ship traffic, and the tide was pushing the oil away from shore, Romero said.

The cause of the rupture was under investigation.