The mysterious gray goo that killed 170 seabirds in the San Francisco Bay Area has been identified as a synthetic oil.

Scientists at state and federal laboratories have yet to determine where the sticky gunk that looked like rubber cement came from or exactly how it got into the bay.

Lab officials determined Thursday that the goo that first turned up on shorelines east of San Francisco in mid-January contained a mixture of non-petroleum-based fats or oils.

Non-petroleum oils include synthetic oils, such as silicone fluids, tung oils, and wood-derivative oils such as resin/rosin oils. Animal fats and oil, and edible and inedible seed oils from plants are included too.

The odorless substance sapped the seabird's ability to stay warm, float or fly. More than 300 birds were also captured alive. Ninety-one birds remain at a rehabilitation center waiting for release.