Changes of TPH concentrations during the crude oil degradation by both isolates and their mixture are presented in Fig. 2. Degradation of crude oil were above 80% after incubation of 20 days for both bacterial strains and their mixture. The maximum degree of removal was achieved after 1-4 days (above 50%). Afterwards removal values decreased progressively and finally approached above 80%. Under the experimental conditions Alcaligenes piechaudii SRS was a better degrader than Ralstonia picketti SRS. The mixture of the isolates enhanced slightly the degradation efficiency of crude oil.