An oil sample from the Tertiary reservoir in the well BH-22 in Bai –Hassan Oil Field, Northern Iraq has been analyzed by the means of GC and GC/MS. The identified biomarkers and the stable carbon isotopes indicated a low salinity marine carbonate depositional environment for the precursor organic matters of the oil. CPI, 20S/ (20S+20R) C29ST, ββS/ (ββS+ααR) C29ST and other maturity biomarkers showed a moderately mature oil. Non effect of biodegradation has been found out from the ratios of P1, P2, and P3 and from the absence of 25-Norhopane biomarker. A Star diagram has been drawn for the analyzed oil sample as a finger print using C9 – C20 alkanes.