Placement of a saltwater disposal well (SDW) within the footprint of a mature oil and gas (O&G) exploration and production region is a bad idea. A long history of O&G exploration means many deep wells (> 5,000 ft below ground surface, bgs) have been installed, and many of these wells were installed prior to modern construction standards, permitting requirements, and data tracking capabilities. Consequently, there are likely to be many poorly constructed and unplugged deep wells whose locations have been forgotten. The purpose of deep well disposal is to segregate the disposal fluids, i.e., harmful waste, from the environment which includes underground sources of drinking water (USDW). Sequestration and containment of harmful wastes is eliminated when there are unknown deep and improperly abandoned wells that pierce containment. This issue of lack of adequate confinement for deep waste disposal is common in Texas because of the prevalence of legacy O&G fields and relatively relaxed permitting requirements for SDWs. This paper demonstrates that locating Texas Class II disposal wells (SDWs) and O&G activities within the same area increases waste containment failure likelihood by 2 times relative to generic SDWs in other states and 100 times relative to Class I hazardous waste (Class IH) injection well systems.