Abstract: Dissolved heavy hydrocarbons(>C;) have been separated from Tarim basin's oilfield waters by quantitative extraction of organic solvent. Part constituents of the heavy hydrocarbons have been determined based on GC, GC/MS and carbon stable isotopic analyses, which are mainly middle to long chain n- alkane, i-alkane, some alkyl toluenes and alkyl cyclohexanes. Their constituents are similar to that of oil which suggests that there be direct relationship between the origin and distribution of dissolved heavy hydrocarbon in oilfield waters and oil reservoirs. The study on the dissolved organic compounds in oilfield waters can get the informat ion about oil and gas shows; can be used for indicating the existence of oil or gas reservoir nearly and provide a new idea of traling the direction and path of oil and gas secondary migration and accumulation.

Key words: Tarim basin, oilfield water, heavy hydrocarbon, hydrocarbon composition, oil and gas reservoir