ABSTRACT Biodegradation studies was performed to investigate the diesel oil and kerosene degrading ability of two strains of yeast identified as Candida tropicalis and C. utilis and isolated from the vicinity of motor mechanic workshops and a railway station.Each treatment contained 1% (v/v)kerosene or diesel as sole carbon and energy source in mineral salts medium.The influence of cultural conditions such as temperature, pH, medium composition, type of carbon and nitrogen sources were investigated.Under aerobic conditions and after 16 days of incubation, C.tropicalis exhibited a rnrked reduction in the kerosene hydrocarbon components by 88.9% while C.utilis effected a reduction by 70.8%.Similarly, the diesel components were reduced by 91.0% and 63.5% respectively. Stathflically, there were significant differences(p<0.05)in the hydrocathon utilization by the isolates.The optimum conditions for growth and hydrocarbon degradation were pH 6.5 at 30°C for both organisms. Biomass yield obtained for both organisms was higher for diesel than for kerosene.Mixed cultures of the organisms reduced kerosene hydrocarbon components by 91.5% and 94.2% for diesel.Gas chromatographic analysis of residual products of the degradation of kerosene and diesel hydrocarbons showed that bwer carbon number (C8-C9)alkanes were readily depleted in the medium than C10-C20 carbon numbers.The influence of supplemented carbon and nitrogen sources was also examined. Enhanced hydrocarbon utilization was obtained with soya bean meal and potato flour as supplemental nitrogen and carbon sources.The two organisms showed high biosurfactant production and a reduced surface tension to values of 28.9±0.4D/cm and 43.3±0.3D/cm.The biosurfactants were characterized as glycolipids.The observed reduced surface tension, production of biosurfactants and high cell hydrophobicity are the plausible mechanism by which the isolates degraded the hydrocarbons.