Sapropeldominated gas was first found in the Xujiaweizi fault depression zone (XFDZ), Songliao Basin. This study focuses on various deep gases in different areas and their genesis. 35 deep gas samples from 29 wells and 33 deep sourcerock samples from 26 wells in XFDZ north of the Songliao Basin were collected for analysis of stable carbon isotope compositions and hydrocarbon fingerprint chromatogram. The experiment suggests that deep gas contains humic gas, sapropel type gas and organogenic gas, with little or minor abiogenetic alkane gas. Quantitative measurement methods to contribution of various organogenic gas are proposed for the first time in this study and has been verified through experiments. The five genetic type indexes including methane carbon isotope, ethane carbon isotope, methylcyclohexane index, cyclohexane exponent and aliphatic hydrocarbon parameter are used to identify 5 end indexes of humic gas, sapropel type gas and organic anatetic origin gas. The geochemical modeling for genetic type indexes using natural gas blend matching and calculation template using nonlinear mathematical simulation method initially measures the contributions of the three organogenic gases in XFDZ. Experimental results show that besides the contribution of organogenic gas accounting for 81%, which comes from Fangshen 1 well and Fangshen 2 well in the Changde gas reservoir, the average contributions of humic gas, sapropel type gas and organic anatetic origin gas are 62.45%, 25.51% and 12.02%, respectively. Humic gas, sapropel type gas and organic anatetic origin gas contribute distinctively in different regions or intervals. The average contribution of the three organogenic gases in the Shengping-Wangjiatun region is 61.63%, 20.94% and 17.29%, respectively; that in the Changde area 73.74%, 14.48% and11.77%; that in the Xingcheng-Xudong and central eastern areas of the fault zone 51.98%, 40.99% and 7.01%. From Shengping to Wangjiatun, and from Dechang to the Xingcheng-Xudong region, the contribution of organic anatetic origin gas decreases while that of sapropel type gas increases, with the contribution of organic anatetic origin gas in some intervals exceeding 40%, and some reaching to 79%. All these features coincide with the type Ⅱ organic development of hydrocarbon source rock in the middle of the fault depression zone, and geologic features of the fault depression zone. This area is characterized by vertical migration of gas from the underlying source rock, with lateral migration as secondary control on the formation of gas reservoir.