Biodegradation of crude oil and 7 different distillation products by Ralstonia picketti SRS and Alcaligenes piechaudii SRS was investigated. Crude oil degradation was above 80% after incubation of 20 days for both strains and their mixture. Removal of short/long alkanes and BTEX investigated was different, from 97% (for hexane degraded by the mixture of the isolates) to 22% (for tridecane degraded by Alcaligenes piechaudii SRS). Hexadecane, pristane and cyclohexane were degraded with high efficiency between 72-91%. Among BTEX, toluene was degraded very well by both strains and their mixture. Benzene and m+p-xylenes were efficiently degraded by the mixture of the isolates, 78% and 87%, respectively. Degradation of light boiling fractions achieved 80-100%. On the other hand, degradation removal of heavy, high boiling fractions was lower, and reached between 10-81%. The mixture of the isolates enhanced slightly the degradation efficiency of crude oil and its distillation products. Changes in crude oil toxicity as a function of biodegradation activity were also undertaken. Slight luminescence inhibition as a measure of toxicity was found during the experiment time. The samples were not found to be toxic to Vibrio fisheri during the crude oil biodegradation. The luminescence inhibition could be due to the presence of toxic intermediates produced during biodegradation.