Screening of 45 hydrocarbon-degrading bacteria demonstrated that 75% of strains growing on hexadecane were able to produce surfactants. The studied strains were separated into the following types: (i) those accumulating surfactants associated with the cell wall (endotype) and (ii) those excreting surfactants into culture medium (exo-type). The most active exo-type strains growing on hexadecane excreted formate, acetate, succinate, beta-alanine, beta-o-butyrate, trehalose and fatty acids into the medium. In all studied exo-type strains growing on hexadecane, surfactants were fatty acids as intermediate products of hydrocarbon degradation. During growth on naphthalene, the exo-type surfactants were probably caprylic acid and its unsaturated analogues as products of biosynthesis de novo. (c) 2005 Published by Elsevier Ltd.