BILLINGS, Mont. (AP) — Montana officials are investigating several sites where they've found suspected oil left over from an Exxon Mobil pipeline break last year, but say at least one such site has turned out to be crude-free.

The July 1 accident spilled an estimated 63,000 gallons of crude into the Yellowstone River near Laurel.

Montana Fish, Wildlife and Parks spokesman Bob Gibson said Tuesday agency workers found sheens or other evidence of oil at several sites downstream of the spill so far this spring.

Department of Environmental Quality scientist Laura Alvey says that includes a sheen she saw last week on an island east of Laurel that was unquestionably from oil.

Alvey says recent tests on water and sediment samples from a riverfront residence near the spill site were negative for crude contamination.