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Among six crude oil-degrading yeasts that were isolated from an oil-polluted area in the Persian Gulf, two yeast strains showed high degradation activity of aliphatic hydrocarbons. From an analysis of 18S rRNA sequences and biochemical characteristics, these strains were identified as Yarrowia lipolytica strains PG-20 and PG-32. Gas Chromatography (GC) analysis of the crude oil remaining in the culture medium after 1week at 30°C showed that the strains PG-20 and PG-32 degraded 68% and 58% of crude oil, respectively. The optimal growth condition and biodegradation of hydrocarbons was in ONR medium with an acidic pH (pH5). These two strains may degrade aliphatic hydrocarbons more efficiently than aromatic hydrocarbons, although strain PG-20 had better degradation than strain PG-32. The two Y. lipolytica strains reduce surface tension when cultured on hydrocarbon substrates (1% v/v). These …