Nitrate-reducing bacterial strains (Pseudomonas sp. BS2201, BS2203 and Brevibacillus sp. BS2202) isolated from petroleum-contaminated soil were capable of degrading petroleum hydrocarbons under aerobic and anaerobic conditions. Under aerobic conditions (a IO-day experiment in liquid media) the strains degraded 20-25% of the total extractable material (TEM), including up to 90-95% of all alkanes analyzed (n-C-10-C-35). Under anaerobic conditions (a 50-day experiment) these organisms degraded 15-18% of the TEM, 20-25% of some alkanes, and 15-18% of selected polycyclic aromatic hydrocarbons. The strains also degraded saturated hydrocarbons under anaerobic conditions in the absence of nitrates as electron accepters. (C) 2000 Elsevier Science Ltd. All rights reserved.