Five experiments were done to study the effect of nutrient application to soils contaminated with engine oil on the stimulation of microbial activity and their biodegradation of engine oil. Adding a nutrient solution to soils taken at three different locations enhanced the microbial activity of the soil. This was shown through the increase of the first order reaction rate of the biodegradation process. The first order reaction rate increased for the three soils from zero to 0.014 (day ^-1),  from 0.0069 (day ^-1) to 0.0139 (day ^-1),  and from 0.0211 (day ^-1) to 0.0336 (day ^-1), with the consequent decrease of the half life time from infinity to 48.8 days, 100 to 49 and from 32 to 20 for the three soils respectively. Another experiment was done on the effect of adding more extra oil on the biodegradation of the engine oil. There was no effect in the earlier stages of degradation while it increased the biodegradation in later stages, probably due to the increase in count of oil bio-degraders from 5.7 x 10⁶ to 2.0 x 10⁸ and from 1.5 x 10⁴ to 1.6 x 10⁷ cfu g^-1, respectively after 3 weeks, during which about 56 % of engine oil was oxidized. Four local different bacterial isolates were used to check for their ability in degrading the oil. There were large differences in the bacterial efficiency of bioremediation. The half life time decreased by about 60 %, 83 %, 13% for the first, second, third with comparison to the fourth strain which is least efficient. The half life time of the fourth one was 1.74 days. The implications of this are discussed in the conclusions.