Abstract: Based on the analysis of deep oversaturated coalbed methane (CBM) reservoirs, the following understandings are obtained. (1) As the buried depth of coal seam increases to a certain depth, the positive effect of coal rank and formation pressure on adsorption is less than the negative effect of temperature on adsorption, as result of which the adsorption gas is gradually saturated (adsorption saturation of 100%) and enters in the stage of in-situ free gas occurrence, thus forming deep oversaturated CBM reservoirs. The formation pressure and temperature keep increasing with the buried depth, and this objective law provides natural conditions for the formation of oversaturated CBM reservoirs in deep strata of the basin. (2) The critical depth of oversaturated CBM reservoirs varies in different basins, and the critical depth difference of oversaturated CBM reservoirs is determined by the basin geothermal gradient and pressure gradient. Abnormal high pressure and temperature (such as the high temperature caused by volcanic thermal events) can reduce the critical depth of oversaturated CBM reservoirs. (3) Deep oversaturated CBM reservoirs have the advantages of short gas breakthrough time, full utilization of formation energy and low cumulative water production in the exploitation, which is expected to become an important field of CBM exploration and development in the future, possessing broad exploration prospects in China's large-scale basins with deep coal seam burial conditions. The understandings of deep oversaturated CBM reservoirs come from the analysis of static data and production dynamic data on-site, reflecting the epistemological view that the knowledge originates from practice and in turn serves practice. This has great significance for guiding deep CBM exploration and development.