This report documents research done on the mature and prolific McAllen Ranch gas field in South Texas, as part of the Secondary Gas Recovery (SGR) project funded by the Gas Research Institute, U.S. Department of Energy, and State of Texas.ABSTRACTA Secondary Gas Recovery project study in South Texas demonstrated that reservoir compartmentalization can result in reserve growth in a mature gas field. McAllen Ranch is an important field in that it typifies South Texas gas fields that produce from the deep, overpressured sandstone reservoirs of the Oligocene Vicksburg Formation.