Two new strains of fermenting bacteria were isolated from oily sludge under conditions of enhanced salt concentration (approx. 8% w/v) and temperature (50 degrees C). They produced considerable amounts of surface-active compounds that were detected by a newly developed quick and easy half-quantitative test of emulsion stabilization, and were quantified by tensiometry. The chemical structure of the surfactant is unknown. The strains grew fast with inexpensive substrates such as sugars and might be of interest for application in microbially improved oil recovery. Morphological, cytological, and physiological characterization allowed affiliation of the two strains to the genus Bacteroides.