The biodegradability of anionic surfactants in oilfield detergents was investigated using water samples from the New Calabar River and Tap water. The detergents analyzed were DD-Y, DG-X, SUR-500, SW-1000 and Bio-Boost. The anionic surfactant, Sodium dodecyl sulphate (SDS) was employed as a reference. The total heterotrophic counts in the water samples were determined using the spread plate technique while the detergent-utilizers were investigated using Mineral salt agar. Biodegradation was evaluated by monitoring Methylene Blue Active Substance (MBAS) using the “River die-away” method. The percentage MBAS remaining, after the 28 day study period, in increasing order was SDS< SUR-500< SW-1000< Bio-boost< DD-Y< DG-X; SDS was the most biodegraded. SUR-500, SW-1000 and Bio-boost supported the highest growth of utilizers. The detergent-utilizing bacteria isolated belonged to the genera Proteus, Acinetobacter, Enterobacter, Staphylococcus, Bacillus, Pseudomonas, Arthrobacter, Corynebacterium and Micrococcus. A steady increase in total viable count, pH and optical density was observed during biodegradation. The detergents tested could be considered biodegradable as they had an average of 91%-97% primary biodegradation at the end of the 28 day test period which is within the biodegradability standards set by the Soap and Detergent Association (SDA) and the Organisation for Economic Co-operation and Development (OECD).