Authorities say remnants of oil are coming from an offshore petroleum platform off the coast of Louisiana.

The Mariner Energy Inc. oil rig exploded Thursday, leaving a mile-long oil sheen spreading into the Gulf. Coast Guard Petty Officer Bill Coklough said the sheen is about 100 feet wide.

A commercial helicopter pilot flying near the rig reported the explosion around 9 a.m. CT. The platform is located just south of the Vermilion Bay, west of BP's massive oil spill. All 13 people on the rig survived.

Authorities are unsure if the oil sheen is coming from barrels of oil stored on the rig or if from a leaking well.

Unlike the BP oil spill, the Mariner Energy rig is in relatively shallow water -- about 340 feet deep.

The cause of the explosion is still unknown.