Oil spilled off the California coast in May migrated more than 150 miles to mix with oil from natural seeps, Plains All American Pipeline said.
Plains said it received a portion of the lab results from samples collected along California beaches after the May 19 release from its Line 901 in Santa Barbara County.
"Analysis of initial samples suggests that some of the Line 901 released oil appears to have migrated over time to beaches in Ventura and Los Angeles Counties along with oil from other sources, some of which has been confirmed to be from natural oil seeps," the company said in a statement emailed to UPI.
Response crews last week started removing containment boom deployed off the Santa Barbara coast. A unified command set up to deal with the release said June 13 there were no signs of sheen for several days.
Crews continue to remove oiled vegetation and soil and recover soiled wildlife. As of Sunday, a total of 192 birds and 103 mammals have been recovered dead.
Federal investigators found "extensive" corrosion on the breached pipeline, with walls degraded by as much as 74 percent of their original thickness in some locations.
The pipeline system leaked as much as 2,500 barrels of oil in Santa Barbara County. About 500 barrels may have reached the waters off the coast of Refugio State Beach in a release the Environmental Protection Agency said was the worst spill in California in the last 25 years.
