Natural gases from the Qiudong and Hongtai gas fields in the Taibei sag in the Turpan-Hami Basin of China were analyzed for stable hydrogen and carbon isotopic characteristics, to investigate the origin of the gas and the gas-source correlation. Natural gases from the two gas fields are dominated by alkane gases with methane content varying from 81.61% to 92.57%. Dryness ranges from 0.76 to 0.93, indicating an abundance of wet gas. The carbon and hydrogen isotopic compositions of the methane vary from -39.8 parts per thousand to -42.6 parts per thousand and from -263 parts per thousand to -279 parts per thousand in the Qiudong gas field, respectively, and from -37.7 parts per thousand to -39.0 parts per thousand and from -250 parts per thousand to -257 parts per thousand in the Hongtai gas field, respectively. All gases have a characteristic carbon and hydrogen isotopic distribution pattern among the C-1-C-5 alkanes, in which delta C-13(CH4) < delta C-13(C2H6) < delta C-13(C3H8) < delta C-13(C4H10) < delta C-13(C5H12), and delta H-2(CH4) < delta H-2(C2H6) < delta H-2(C3H8). Both the stable carbon and hydrogen isotopic compositions of the gases and the hydrogen isotopic value of the formation water suggest that gases in the two gas fields are coal-derived without admixtures with gases of other origin. According to the calculation with empirical delta C-13(CH4)-R-o% relationship, the thermal maturity (vitrinite reflectance R-o%) of the source rocks is up to 0.76% in the Qiudong area and up to 0.86% in the Hongtai area, which are in the oil window and approaching the start of major thermogenesis at the top of the maturity range. Since the gases in the Hongtai gas field are relatively more enriched in C-13 and H-2, combined with the local geological thermal evolution history, it is concluded that the gases in the two gas fields were derived from the Lower Jurassic Badaowan source rocks. The heavier hydrogen and carbon isotopes of the gases from the Hongtai gas field are interpreted as a product of higher thermal maturity of the source rocks. This is in consistent with the thermal maturity of the local source rocks. The modern thermal maturity of the top of the Badaowan Formation is around 0.8% in the Qiudong area and around 1.0% in the Hongtai area. The combined use of both carbon and hydrogen isotopes is of high value in providing information on gas origin and gas-source correlation, which will be very useful for future gas exploration. (C) 2015 Elsevier B.V. All rights reserved.