Abstract: An investigation of bacterial population of an oilfield wastewater was done for 5 months and 2 seasons (dry and wet) in 2009. Freshly-produced oilfield wastewater samples were analyzed for Aerobic Heterotrophic Bacteria (AHB) and Hydrocarbon-utilizing Bacteria (HUB) using standard procedures. Mean monthly counts of aerobic heterotrophic bacteria (x104 cfu mL-1) and hydrocarbon-utilizing bacteria (x103 cfu mL-1) were: Dec. 13.2±9 and 0.66±0; Jan. 15.2±13 and 13.4±12; Mar. 8.4±6 and 0.18±0; Jul. 14.5±9 and 0.11±0; Aug. 9.9±4 and 0.17±0, respectively. Dry season recorded mean counts (x104 cfu mL-1) of 14.3±8 (AHB) and 7.0±9 (HUB) while wet season had mean counts (x103 cfu mL-1) of 12.3±5 and 0.14±0 aerobic heterotrophic bacteria and hydrocarbon-utilizing bacteria, respectively. Fourteen species of heterotrophic bacteria isolated included Pseudomonas (16%), Klebsiella and Staphylococcus (13%), Corynebacterium, Enterobacter and Proteus (9%), Acinetobacter and Micrococcus (6%); Alcaligenes, Bacillus, Chromobacterium, Citrobacter, Clostridium and Flavobacterium (3%). Eleven species of hydrocarbon-utilizing bacteria isolated included Acinetobacter and Bacillus (15%), Klebsiella, Micrococcus, Proteus, Pseudomonas and Staphylococcus (10%), Alcaligenes, Corynebacterium, Flavobacterium and Serratia (5%). Monthly fluctuations of bacterial population occurred in the wastwater and number of bacteria were higher in dry season than wet season. Bacteria survive in wastewater and hydrocarbon-utilizing bacteria can be isolated from the wastewater and used for clean up of petroleum contaminated soil.