This project contains maps of potential regions of pervasive gas (extensive underpressured gas with updip water) in the Muddy and Shannon Zones in the study area north of the Black Hills in Montana and South Dakota. This study aims to identify structures where gas is potentially flushed from conventional structures by strong hydraulic gradients related to recharge through the Muddy and Shannon Zone outcrop belts. This study further identifies regions where the hydrodynamic gradient might increase the trapping potential in conventional structures by favourably tilting the gas/water contacts.