The degradation of petroleum biomarkers was examined using mixed cultures of microorganisms enriched from surface soils at four different hydrocarbon-contaminated sites. These cultures degraded C30 17alpha(H),21beta(H)-hopane and the C31-C34 extended hopanes in Bonny Light crude oil after 21 days of incubation at 30 degrees C. The C35 extended hopanes were conserved, and no 25-norhopanes were detected during the incubation. Denaturing gradient gel electrophoresis (DGGE) analysis of the enrichment cultures demonstrated distinct microbial community profiles. Additional studies with the LC culture demonstrated a consistent biomarker degradation pattern after growth on three crude oils: a Nigerian Bonny Light crude, a Venezuelan crude oil, and Alaskan North Slope 521. The onset of biomarker degradation was observed between days 14 and 21 but only at 30 degrees C and at oil concentrations below 6 mg/mL. The biomarker profiles following degradation by these enrichment cultures are similar to numerous field observations and may represent the dominant biodegradation pattern found in many hydrocarbon-contaminated aerobic surface environments.