1�� Department of Geochemistry��Yangtze University��Jingzhou 434023��Hubei��China; 2�� Key Laboratory of Exploration Technologies for Oil and Gas Resources��Ministry of Education��Yangtze University�� Jingzhou 434023��Hubei��China;

Gas Hure Oilfield is the biggest one in the Qaidam Basin�� Through intensive sampling and GC-MS analysis�� the authors analyzed the geochemical characteristics of the crude oils in the Gas Hure Oilfield�� The results show that the crude oils have even-odd carbon predominance for n-alkanes�� In shallow reservoir��part of crude oils suffered biogenic degradation�� As for normal oils��they have low Pr /Ph ratios with abundant gammacerane and C35 homohopane��which indicate that the crude oils are formed in strong reducing salt water environment�� Compared deep ( E13 ) reservoir with shallow ( N1 �� N12 ) reservoir��the ancient salinity of sedimentary environment of N1--N12 crude oils is slightly higher than that of E13 crude oils; the C �� 21 /C + 22 ratios of crude oils are 1. 02-1. 71 with a higher abundance of C27 sterane��which shows that their mainly origin matrix are bacteria and algae; the C29 sterane 20S /( 20S + 20R) is generally low��the ratio in deep E13reservoir distributes between 0. 31 and 0. 40��but in shallow reservoir is relatively low with 0. 29-0. 36�� At the same time��C29 sterane αββ/( αββ + ααα) and Ts /Tm both are extremely lower�� All the above show that the crude oils in Gas Hure are mainly low mature oils��although the maturity of deep reservoir crude oils is slightly higher than shallow one��