Lactobacillus delbrueckii cultured with peanut oil cake as the carbon source yielded 5.35 mg ml(-1) of biosurfactant production. Five sets of microcosm biodegradation experiments were carried out with crude oil as follows: set 1 - bacterial cells + crude oil, set 2 - bacterial cells + crude oil + fertilizer, set 3 - bacterial cells + crude oil + biosurfactant, set 4 - bacterial cells + crude oil + biosurfactant + fertilizer, set 5 - with no bacterial cells, fertilizer and biosurfactant (control). Maximum degradation of crude oil was observed in set 4 (75%). Interestingly, when biosurfactant and bacterial cells were used (set 3), significant oil biodegradation activity occurred and the difference between this treatment and that in set 4 was 7% higher degradation level in microcosm experiments. It is evident from the results that bio-surfactants alone is capable of promoting biodegradation to a large extent without added fertilizers. (C) 2010 Elsevier Ltd. All rights reserved.