The soil-isolated strain XP was identified as Rhodococcus erythropolis. R. erythropolis XP could efficiently desulfurize benzonaphthothiophene, a complicated model sulfur compound that exists in crude oil. The desulfurization product of benzonaphthothiophene was identified as alpha-hydroxy-beta-phenyl-naphthalene. Resting cells could desulfurize diesel oil (total organic sulfur, 259 ppm) after hydrodesulfurization. The sulfur content of diesel oil was reduced by 94.5% by using the resting cell biocatalyst for 24 h at 30 degrees C. Biodesulfurization of crude oils was also investigated. After 72 h of treatment at 30 degrees C, 62.3% of the total sulfur content in Fushun crude oil (initial total sulfur content, 3,210 ppm) and 47.2% of that in Sudanese crude oil (initial total sulfur, 1,237 ppm) were removed. Gas chromatography with pulsed-flame photometric detector analysis was used to evaluate the effect of R. erythropolis XP treatment on the sulfur content in Fushun crude oil, and it was shown that most organic sulfur compounds were eliminated after biodesulfurization.