Abstract: It was usually thought that extrusive rocks were not gas source of carbon dioxide reservoirs, because most of the gas was released directly into atmosphere in the cooling process. Whereas recently some researches indicated that CO2 gas of Changdedong gas reservoir was mainly adsorbing gas in volcanic rocks, and post-release of adsorbing gas was important to form the gas reservoir. In order to evaluate the potential and possibility for adsorbing CO2 gas forming gas reservoirs quantificationally, low-temperature (250℃) degassing experiments of volcanic rocks in northern Songliao basin were done. The amounts of released volatile are 0.0299~0.0790ml/g, and those of CO2 are 0.0218~0.0706 ml/g (0.429~1.387wt％). The relationship of the amounts between volatile and carbon dioxide is positively linear. The main component of volatiles is carbon dioxide, and the secondly is N2, and some associated components are deoxidized gases, such as H2, CO, CH4, as well as fewer amounts of low-carbon alkanes. Both the content in volatile and degassing amount of CO2 have an inverse relation with the content of hydrocarbon. There is a negative correlation between the CO2 degassing amount and SiO2 content of volcanic rocks. Volcanic rocks, particularly the basic ones, can adsorb vast amount of carbon dioxide and act as the major gas source rocks. When forecasting geological resource of carbon dioxide, the amount of volatile of volcanic rocks at 250℃ can be treated as the lower limit of the content of volatile and remnant CO2, while the content of total carbon as the upper limit of the amount of degassing CO2.