The objectives of this study were to determine and compare the petroleum biodegradation efficiencies of three different bacterial consortia adapted to oil field. For this purpose, petroleum-contaminated waste mud sample was enriched in Bushnell Haas medium with 1% petroleum. Six different bacterial strains (four Gram-positive and two Gram-negative) were isolated from the enriched sample, and bacterial strains were identified with phenotypic and genotypic analyses. Each bacterial strain was evaluated in terms of biodegradation capacities by colorimetric analysis with the DCPIP redox indicator. Petroleum biodegradation efficiencies of three different consortia were investigated by gravimetric and GC-MS analyses. Consortium 1, consisting of Bacillus subtilis, Leuconostoc mesenteroides, Bacillus halotolerans, Enterococcus casseliflavus; consortium 2, consisting of Klebsiella pneumoniae and Pannonibacter phragmitetus; consortium 3, consisting of Bacillus subtilis, Leuconostoc mesenteroides, Bacillus halotolerans, Enterococcus casseliflavus, Klebsiella pneumoniae and Pannonibacter phragmitetus, were used in petroleum biodegradation. According to the results of gravimetric analysis, biodegradation of petroleum was 48%, 77% and 82% for consortium 1, consortium 2 and consortium 3, respectively. The results of GC-MS analysis revealed that removal of long-chain n-alkanes (C-23-C-32) was in the range of 35-58% by consortium 1; 56-67% by consortium 2; and 63-74% by consortium 3. It was emphasized that consortium 2 was more effective in biodegradation of petroleum than consortium 1. This study clearly demonstrated that consortium 3 is most effective in biodegradation of petroleum. This is assumed to be due to the synergistic effect between Gram-positive and Gram-negative bacterial strains. Furthermore, consortium 3 has been found to be very successful despite the shorter incubation period compared to other consortia in the literature. In this context, it is believed that the use of consortium 3 will contribute to the bioremediation of petroleum on a large scale.