Abstract Oil pollution in Izmit Bay was investigated after the fire of Tiipras refinery that followed the earthquake in 17 Aug. 1999. The highest oil pollution was found in Eregli on surface water (covered wholly by oil) and in Ulasli as I79.2 mg/L in 24-27 Aug 1999 and fell to 425 µg/L in 15-l9Aug 2000. The maximum oil level in surface water in eastern part as 53.2-µg/ L, the central part as 1688 µg/L, in the western part as 463.6 µg/L and one year later it was changed as 10.40 pg/L, 13.68 µg/L and 12.98 µg/l, respectively, The determination of oil origin was made by the fingerprinting analysis method and. found that its origin was TUpras refinery accident. The results of UVF and GC/MS and fingerprinting analyses are reported in this paper.