Although conditions in the Mohe permafrost of northeastern China, including temperature, pressure, groundwater, gas migration, and host reservoirs, are favorable for gas-hydrate accumulation, no gas hydrates have been found because the gas availability remains problematic. Therefore, gas availability in this region has become a key research topic. In this study, the characteristics and distribution of hydrocarbon gases in the Mohe permafrost were analyzed to examine sources of potential gas-hydrate formation. For this purpose, 378 gas samples were analyzed for molecular and carbon and hydrogen isotope compositions. The results show that hydrocarbon gases mainly comprise methane (greater than 99%) at burial depths less than 1000 m. At depths greater than 1000 m, heavy hydrocarbons account for more than 2%, and the gas-dryness coefficient and C1/(C2+C3) ratios tend to decrease with increasing depths because of the chromatographic effect of upward gas migration or diffusion. The carbon isotope values of methane show an increasing trend with depth, whereas those of hydrogen isotopes show the opposite trend. The carbon and hydrogen isotopes of methane show a negative correlation, which is likely attributable to the mixing of 13C-depleted and D-enriched methane (produced mainly via carbon dioxide reduction at shallow depths) with 13C-enriched and D-depleted methane (formed via acetate fermentation at greater depths). From the gas and isotope compositions, microbial gas was inferred to dominate intervals at depths less than 1200 m. Mixed gases of microbial and thermogenic origins may occur at intermediate depth intervals between 1200 and 2300 m. Thermogenic gases are distributed at greater depths, with their formation facilitated by higher temperatures. Thus, gases for potential gas-hydrate formation may contain a combination of microbial and thermogenic gases migrated from deep intervals. Finally, potential concentrated hydrate deposits are believed to occur along gas-migration pathways, such as faults, in the Mohe Formation of the central-northern part of the Mohe Basin. In the future, fault zones, especially reverse faults and their adjacent fractures, and permeable sandstones in the Mohe Formation of the central-northern part of the basin should be the main target of gas-hydrate exploration.