The contamination of soil and groundwater by hazardous chemicals has become a major concern due to the associated risks to human health and the environment. The ability of Pseudomonas putida isolated from a petroleum refinery effluent to degrade diesel was assessed in this study. The effluent sample was collected from the treatment plant in the Kaduna Refining and Petrochemical Company (K.R.P.C), Nigeria. The physicochemical properties and heavy metal content of the effluent was determined, and three strains of Pseudomonas putida were identified among the bacteria isolated using conventional biochemical and phenotypic tests. The strain showing the highest degradation potential after screening was selected for the final biodegradation studies. The ability of the selected strain of Pseudomonas putida (C15a) to utilize the hydrocarbons in diesel was assessed over a period of eighteen days, and monitored on a three-day interval by evaluating the pH, hydrocarbon utilizing bacterial count and oil and grease content. It was observed that the organism was able to utilize diesel for its metabolic needs as shown by the increase in hydrocarbon utilizing bacterial (HUB) count and corresponding decrease in oil and grease content as well as pH. The highest hydrocarbon utilizing bacterial count was observed at day 15 (1.85 x 10 7 CFU/mL) with highest hydrocarbon degradation occurring at day 18 (98.3%). The strain of Pseudomonas putida (C15a) isolated in this study can be used as a candidate for further bioremediation studies on petroleum.