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 of Flavobacterium and Brevibacterium when growing on oil. Cells of Flavobacterium sp. had smaller inclusions when grown on marine agar, while inclusion bodies were not found in Brevibacterium sp. grown on marine agar. Sudan black B staining indicated the inclusions are stored lipids.