Abstract: A novel strain of Pseudomonas aeruginosa, designated as strain SB-1, is capable of growth on hydrocarbon substrates having 10 to 32 or more carbon atoms, during which growth there is secreted into the culture medium an emulsifier which can be recovered and used for such applications as reducing the viscosity of crude oil in secondary recovery methods, as well as in oil spill management and the cleaning of oil-contaminated vessels and pipelines. A novel mutant strain of P. aeruginosa SB-1, designated SB-3, has the property of growing on solid (C.sub.20 +) paraffins but not on liquid alkanes. The selective degradation by strain SB-3 of the solid paraffinic components in crude oil is advantageous in reducing the viscosity of the oil for improving the recovery thereof from oil wells. A novel revertant strain of P.