The Orange County Transportation Authority's Cleaner Air through Reduced-Emission Systems (OCTA CARES) program is evaluating several options for reducing transit bus emissions. OCTA initiated the program in response to the 1991 Federal and California heavy-duty emission standards, and potential South Coast Air Quality Management District (SCAQMD) requirements for transit fleets to utilize clean alternative fuels. Through the OCTA CARES program's Comparative Evaluation of Clean Fuels demonstration project, alternative fuels such as methanol, compressed natural gas (CNG), and liquefied petroleum gas (LPG) are being demonstrated and evaluated in Gillig Phantom buses equipped with Cummins L10 engines. Data are being collected on all aspects of on-road bus operation and performance, including fuel economy, fuel prices, maintenance, and road calls. In addition, exhaust emissions - oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), particulate (PM), and formaldehyde - are being measured through chassis dynamometer testing. This paper discusses the results to date of the Comparative Evaluation of Clean Fuels project, and summarizes other current and future projects in the OCTA CARES program.