The biodegradation of diesel fuel, crude oil and used motor oil was evaluated in the presence of 0, 10, 100, 500, and 1,000 mg L-1 of lecithin, Triton X-100 and Tween 80 at 25°C. CO2 evolution was measured from bubbler tubes containing 20 ml of 0.1% yeast-extract (YE) medium, surfactant, and 2 ml of petrochemical as the principal carbon source. Sixty one microbial isolates from various sources were evaluated. From this screen, four were chosen for further studies. Diesel fuel degradation by Yarrowia lipolytica CP.D-N exhibited optimum activity with Tween 80 and low levels of Triton X-100. Low levels of lecithin were inhibitive. Degradation of crude oil by Bacillus sp. SH.7.C-P was enhanced by lecithin. Crude oil degradation by Y. lipolytica CP.D-N was higher than that of Bacillus SH.7.C-P and inhibited by Tween 80. Used motor oil degradation by Rhodococcus equi MO.M-N was enhanced by lecithin, whereas used motor oil degradation by R. equi CP.M-P was inhibited by Triton X-100;Diesel fuel biodegradation by Yarrowia lipolytica CP.D-N was further evaluated in the presence of soybean, rice and oat hulls (1 g per 20 ml media) pre-coated with 1,000 mg surfactant kg-1 hull. Two procedures were used: (a) hulls were added to the YE medium, then diesel fuel was added; and (b) the hulls were soaked in 2 ml of diesel fuel and then YE medium was added. CO, evolution increased in bubbler tubes with both Yarrowia lipolytica CP.D-N and diesel for both procedures, however, GC analysis revealed no enhancement in diesel fuel degradation. Pre-exposure of the hulls to diesel fuel using the second procedure reduced the extent of diesel fuel removal for most treatments;Soybean hulls were pre-coated with a 5-ml suspension containing 100 mg surfactant kg-1 hull and Y. lipolytica CP.D-N (2.4x109 g-1 hull). The presence of surfactants and Y. lipolytica CP.D-N did not enhance diesel fuel degradation based on CO2 evolution;This research gives evidence that lecithin may promote the bioremediation of used motor oil and crude oil. Triton X-100 exhibited greater emulsification, however, this often corresponded to greater inhibition.