Six strains of Sphingobacterium thalpophilum were isolated from a compost mixture enriched with oleic acid. These strains converted oleic acid to 10-ketostearic acid (10-KSA; 87-94% of the total conversion product) and to 10-hydroxystearic acid (10-HSA; 6-13%) exhibiting three levels of total product yields. The predominant production of 10-KSA by these new S. thalpophilum isolates is in contrast to strain 142b (NRRL B-14797) previously isolated from a commercial compost, which produces exclusively 10-HSA. The production yield of greater than 75% 10-KSA was achieved in 36 h, acting on 0.26 g of oleic acid in 30-ml fermentation broth incubated with agitation at 28 degrees C. For easy maintenance, fast-growth, and high bioreactivity, these S. thalpophilum strains are suited for developing a large-scale production of 10-KSA and 10-HSA.