Nonionic surfactants increase the rate of selective hydrocarbon utilization byAcinetobacterSL1. Within an homologus series of nonionic surfactants, growth on and utilization of a model oil byAcinetobacterSL1 is dependent upon the surfactant hydrophile‐lipophile balance (HLB). Biological effectiveness of the surfactants apparently is related to the degree of micelle formation by the surfactant in the aqueous phase. A simple algebraic expression describing the response ofAcinetobacterSL1 to surfactant concentration gives a measure of the biological effectiveness of an individual surfactant. A cationic and an anionic surfactant inhibited the growth ofAcinetobacterSL1 andPseudomonasSL6 on hydrocarbon substrates. These results are discussed in relation to the selection of suitable detergents for increasing the effective biodegradation of pollutant oil in aquatic habitats.