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A new thinking of gas play in Tawun formation East Java Basin is a result of an integrated research of mud volcano from surface to subsurface data, overpresured and Hele-Shaw analog modeling. The presence of methane gas seepage in the mud volcano proves the existence gas associated with mud and overpressured zones. Analysis of C isotope of samples of gas seepage of mud-volcano indicate thermogenic methane gas at the level of thermal maturity equivalent to the peak of petroleum formation. The overpressured mud zone has a potential to be an unconventional gas reservoir with high gas storage capacity. Mud-gas-play is defined as the accumulated gas which is trapped in the overpressured zone. Gas accumulations have a tendency to be concentrated upper part of overpressure zone. Type of the reservoir and how the gas storage are the differences from the conventional of gas play concept. Reservoir geometry of mud-gas-play is a chamber shaped which cross sediment layer. Gas is trapped in rocks with very low bearing capacity which have high pressure. Two mechanisms of gas trapped in overpressured shale are dissolved and adsorbed. The gas storage capacity of the mud based on adsorption analysis at temperature 65 degree celcius ranges from 812 scf/ton up to 3,217 scf/ton. The unconventional gas reservoirs of overpressured mud zone is proposed as a new hydrocarbon play: mud-gas-play (MGP).