Automatic stop fill (ASF) technology is important for acceptance of alternate motor vehicle fuels. During previous employment with Canadian Gas Research Institute, the authors developed ASF for compressed natural gas (CNG). With that development experience as a starting point, the authors have investigated and analyzed numerous potential solutions to the propane ASF problem. The authors conclude that to implement true ASF, including self-monitoring of the correctness of operation, the propane industry will have to select one method, for use by all vehicles and all dispensers. The authors have developed two different, candidate, fail-safe, self-monitoring, ASF methods for propane.