Diesel degradation and bacterial growth were investigated in soil, marine water, and freshwater ecosystems using Acinetobacter baumannii IITG19, Providencia vermicola IITG20, and their mixed culture. Both bacteria were found to be effective in all three ecosystems, with the best degradation occurring in freshwater. Acinetobacter baumannii IITG19 showed higher degradation (59%, 62%, and 76%) than Providencia vermicola IITG20 (31%, 57%, and 67%) in soil, marine water, and freshwater, respectively. Alkanes showed higher degradation than naphthenes and aromatics for both strains. The mixed culture showed higher diesel degradation efficiency than individual strains in all ecosystems. The overall degradation was similar in soil and marine water (66%), while freshwater showed the highest degradation of 81%. In the presence of the mixed culture, the degradation of alkanes was more than 90%. Bacterial growth was highest in freshwater and lowest in soil for both bacteria and the mixed culture. Metabolite analysis confirmed alcoholic degradation for alkanes and cyclo-alcoholic degradation for naphthenes. The degradation rate for mixed culture was higher than that of both the individual strains. The mixed culture had highest degradation rate constant in freshwater at 0.11 day-1 followed by that in marine ecosystem at 0.078 day-1. The rate constant was lowest for soil ecosystem at 0.066 day-1. Thus the mixed culture showed effectiveness in all three ecosystems, with its highest effectiveness observed in the freshwater ecosystem.