A small number of dolphins that washed up in the Gulf of Mexico have oil on them from a blown-out BP PLC well, but it isn't clear whether the oil was a factor in their deaths, federal scientists said Thursday.

National Oceanic and Atmospheric Administration officials said 293 dolphins—an abnormally high number—have washed ashore along the Gulf coast since late April 2010, when an explosion aboard the Deepwater Horizon, a rig drilling a BP well, sent millions of barrels of oil into the Gulf. Most of the dolphins were dead, NOAA officials said.


In addition, nine other dolphins washed up with a substance on them that NOAA officials suspect was oil, but the source of that substance hasn't been determined, she said.

Tests are underway to try to determine whether the oil spill contributed to the dolphins' deaths, Ms. Mase said.

Hejdi Feick, a BP spokeswoman, said the oil company is aware of the washed-up dolphins and wants "to help in any way we can so the data is thoroughly analyzed to see if a cause can be determined."

Write to Jeffrey Ball at jeffrey.ball@wsj.com