EPA interprets the Clean Water Act definition of oil to include non-petroleum oils, as well as petroleum and petroleum-refined products. 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.

Many non-petroleum oils have similar physical properties as petroleum-based oils; for example, their solubility in water is limited, they both create slicks on the surface of water, and they both form emulsions and sludges. In addition, non-petroleum oils tend to be persistent, remaining in the environment for long periods of time.

Like petroleum-based oils, non-petroleum oils can have both immediate and long-term adverse effects on the environment and can be dangerous or even deadly to wildlife. For example, non-petroleum oils can deplete available oxygen needed by aquatic organisms, foul aquatic life, and coat the fur or feathers of wildlife. When a bird's plumage is coated with non-petroleum oil, their feathers lose their insulating properties, placing them at risk of freezing to death. Birds also can smother embryos through the transfer of non-petroleum oil from the parents' plumage to the eggs.

In addition, birds and wildlife can ingest oil directly and may continue to ingest the oil as they eat if the source of their food consists of fish, shellfish, or vegetation that also are contaminated with non-petroleum oils. Other adverse effects of spilled non-petroleum oil on bird and wildlife include drowning, mortality by predation, dehydration, starvation, and/or suffocation.