This report presents the results of a study to evaluate the potential of increasing the working gas volume of new and existing compressed natural gas (CNG) storage caverns by using an advanced constitutive model for rock salt in the cavern design procedure. Geomechanical finite element analyses were made to determine the minimum gas pressure allowable based on an existing stress-based criterion (the Damage Potential method) and an advanced constitutive model (the Multimechanism Deformation Coupled Fracture (MDCF) model) capable of modeling damage and healing in rock salt. The MDCF model is a constitutive model developed by Sandia National Laboratories and their subcontractors to provide a description of damage, healing, and deformation of salt for safe disposal of radioactive waste at the Waste Isolation Pilot Plant. The MDCF model has the capability to track damage development and healing and to provide a quantitative measure for the damage. Additionally, the healing behavior of the salt (included with the MDCF model) was to be analyzed to determine if complete healing of the damaged rock zone would occur during the time period when the cavern was at maximum gas pressure.