Carbon dioxide layers have been encountered in the Ordovician weathering crust of Lower Paleozoic and in Es₁3 of Paleogene. Based on gas source correlation, it is considered that organic gas source in Es₁3 in Wenliu is from the oil\|type gas formed in the Paleogene clastic rock, while CO₂ is the mixture of the associated CO₂ formed in the secondary hydrocarbon generation of Carboniferous-Permian coal, and the non-organic CO₂ from Ordovician limestone decomposition under high temperatures in Lower Paleozoic. According to the high temperature simulation on the two types of CO2 gas source rock in the Dongpu sag, the gas generation capacity of the Carboniferous Permian coal is 9 times stronger than that of the Ordovician limestone. Seventy to eighty percent of the coal formed gas is methane, with little CO2, while ninety percent of the gas formed in limestone is CO2. Because ofthe gas formed from the same amount of coal and limestone, the contents of CO2 are similar. Coal is the most important gas source rock in the Dongpu sag.