We found for the first time enriched liquid mercury beads in a thermal simulation experiment on humic kerogen extracted from coal, which provided some kind of direct evidence that mercury can be released from coal measure during maturation. In the simulation experiment, mass distribution of liquid mercury beads is between 0.0083 and 0.2242 g; their content in simulated gas ranges from 372.5 to 2776.3 ng/m(3); and their yield was from 0.3102 X 10(-3) to 7.4312 X 10(-3) g/g sample. Along with this thermal simulation experiment and previous studies, three genetic models of mercury in gas reservoirs are summarized: source-rock controlling type, fault-controlling type, and source-rock/fault joint controlling type. Mercury in source-rock-controlling gas reservoirs is mainly derived from source rocks, which are generally coal measures. Mercury in fault controlling gas reservoirs is mainly derived from deep geologic fluids, with relatively small contribution from source rocks. The transitional source-rock/fault joint controlling type mainly develops in tectonic activity zones where source rocks can be either sapropelic or humic. Liquid mercury collected for the first time in a simulation experiment has important theoretical significance for the exploration and development of natural gas, as well as important practical significance for the prevention of mercury accidents in natural gas exploration and production.