A hydrocarbon-degrading bacterium Providencia rettgeri L1 was isolated from petroleum in Shengli oil field, China. The petroleum-degradation characteristics were investigated. The degradation rate of petroleum by the strain was 45.9% in petroleum-mineral medium (5 g/L) in 14 d measured by ultraviolet-visible spectrophotometer. The intracellular crude enzymes of Providencia rettgeri L1 were prepared and supplemented with formate dehydrogenase to construct an enzyme cocktail. The petroleum degradation rate of the cocktail reached 49.5% in 8 h, which was much faster than the strain. The subfraction saturates and aromatics in petroleum were analyzed by gas chromatography and gas chromatography-mass spectrometry, respectively. After degradation for 8 h, the degradation rate of saturates C₁₀-C₄₀ was 50.4%, while the values for short, mid and long-chain saturates were 52.6%, 49.4% and 47.7%, respectively. Biodegradation assessment markers-pristane and phytane, were degraded by 49.3% and 44.9%, respectively. The degradation rate of aromatics was 29.5%. For 2, 3, 4 and 5-ring PAHs, the corresponding values were 47.8%, 24.2%, 29.5% and 19.8%, respectively. Source tracing experiment showed that Providencia rettgeri L1 was more dominant in enriched bacterial suspensions than in petroleum environment, indicating its advantage of rapid proliferation in culture media. This study can provide some insights into fast degradation of petroleum.