A substance thought to be responsible for the deaths of more than 350 birds is probably the same as that which affected hundreds earlier in the year, experts have said.
Scientists from Plymouth University said they were "almost certain" it was polyisobutene (PIB).
It is often used by ships to make their engines work more efficiently.
The Maritime and Coastguard Agency (MCA) said it would try to determine the source.
Hundreds of birds have been found on beaches in Devon and Cornwall since Wednesday.