The aim was to determine the optimum gas turbine powerplant system for a standard six-passenger automobile. The major goals for the gas turbine automobile are (1) it should meet the 1976 Federal Emissions Standards and (2) it should be similar to, or better than, the present automobile with respect to: acceleration; performance; initial consumer cost; fuel economy; and maintenance and repair costs. Through proper design, a gas turbine engine/transmission system can be mass-produced at an estimated cost comparable to a 1970 spark ignition (SI) system. The optimum gas turbine (GT) system has a lower computed average fuel consumption than the 1970 SI system and GT system vehicle acceleration response would equal or exceed the SI system. This study is a limiting case since the engine cycles were not penalized for low-emission combustor designs, because the penalty, if any, has not yet been quantitatively determined. Federal driving cycle emissions were computed for the three candidate systems using data from existing AiResearch engines and analytical techniques. It was found that all of the engines met the CO and UHC requirements with margin, but that none of these conventional combustors met the NOx requirement. Schematics of the systems are presented. The design point characteristics are tabulated. Tables are also presented and discussed of acceleration performance, fuel economy, and costs to the manufacturer and consumer, and of repair and maintenance, and ownership cost. Other figures of the recommended engine system, a mock-up of the engine-transmission system, the demonstration program logic chart, schedule, and milestones are also discussed.