Two species of marine bacteria with the ability to degrade crude oil were compared ultrastructurally after growing in the presence and absence of oil. Large electron-dense inclusions, which were located predominantly at the cell terminus, characterized species ofFlavobacteriumandBrevibacteriumwhen growing on oil. Cells ofFlavobacteriumsp. had smaller inclusions when grown on marine agar, while inclusion bodies were not found inBrevibacteriumsp. grown on marine agar. Sudan black B staining indicated the inclusions are stored lipids.