The efficiency and economics of the Synthane Gasification process are evaluated and discussed in this paper. The efficiency of the Synthane process was determined using the “availability analysis” approach to process evaluation and is given here as an example of the use of that approach. Computer simulation of the Synthane process was used to study the effect of changes in plant operating parameters on both the efficiency and economics of the process. Results of the availability analysis include an overall exergetic efficiency of 61.2 percent for the operation of the Synthane plant with a Pittsburgh Seam feed coal, and an overall exergetic efficiency of 61.1 percent for a Wyodak Seam feed coal. Increasing the ratio of steam to oxygen fed to the gasifier from 6.83 to 10.0 was found to increase the overall exergetic efficiency from 61.2 percent to 64.6 percent with a Pittsburgh feed coal. Utilizing an alternative methanator design similar to one presented in an IGT HYGAS process design was found to increase the overall efficiency to 62.3 percent with the Pittsburgh feed coal and to 61.9 percent for the Wyodak feed coal. The production cost of the synthetic natural gas (SNG) product from the Synthane process was found to be $4.61/GJ with the Pittsburgh feed coal, and $6.23/GJ with the Wyodak feed coal, in third quarter 1979 dollars. The SNG production cost was found to decrease from $4.61/GJ to $4.37/GJ when the ratio of steam to oxygen fed to the gasifier was increased from 6.83 to 10.0. A 50 percent increase in coal cost was found to increase the SNG production cost by 15 percent and 18 percent for the Pittsburgh and Wyodak feed coals, respectively, while a 100 percent increase in coal cost increased the SNG production cost by 30 percent and 36 percent, respectively. Changing to the alternative (HYGAS) methanator design resulted in a decrease of $0.21/GJ in the SNG production cost for the Pittsburg feed coal, and a decrease of $0.26/GJ for the Wyodak coal. The availability approach to the analysis of chemical processes along with a simulation of the process allows intelligent judgements about design modification to be made in the designing process. With the cost of energy becoming a more important design parameter, this approach should provide an important tool to the design engineer.