The use of natural gas as a transit bus fuel is being demonstrated by The Hamilton Street Railway Company. The H.S.R. Is a public transit system operating two hundred diesel buses and fifty electric trolley buses. Six transit buses are operating in daily service using a spark ignited engine dedicated to natural gas fuel. The buses are used primarily for peak period extra service because of insufficient fuel tank capacity.The buses have performed well in service and have exhibited few serious fuel related problems. The fuel consumption however has been considerably higher than anticipated and a series of valve keeper failures occurred in the latter stages of the project.