The objective of this study is to determine the occupant/driver exposure in public transport buses running on biodiesel (B20) and ultra low sulfur diesel (ULSD) buses in the city of Toledo, Ohio. This paper also presents a protocol used for carrying out an experimental study involving continuous monitoring of real-time in-vehicle pollutant concentrations. In-vehicle concentrations of six air pollutants including carbon dioxide (CO2), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particulate matter less than 2.5 micrometer (PM2.5), in addition to two important comfort parameters- temperature and relative humidity are monitored in the two selected buses. This study provides new insights about the indoor environment of public transport buses operating on biodiesel fuels. Results indicate the average 8-hr. exposure of B20 occupants to CO2, CO, NO, NO2, SO2, and PM2.5 to be 559.67 ppm (± 45.01), 18.33 ppm (± 9.23), 5.23 ppm (± 4.49), 0.13 ppm (± 0.05), 0.13 ppm (± 0.01), and 13.75 􀀁g/m3 (± 4.24) respectively while for ULSD bus occupants the average exposures are 632.20 ppm (± 102.70), 8.08 ppm (± 1.41), 0.73 ppm (± 0.21), 0.09 ppm (±0.06), 0.39 ppm (± 0.04), and 13.33 􀀁g/m3 (± 5.49). It was also observed that the mean 8-hour exposure to carbon dioxide and sulfur dioxide were significantly higher inside ULSD buses as compared to B20 fueled buses, while the carbon monoxide and nitric oxide concentrations were higher inside B20 buses. Exposure to nitrogen dioxide and particulate matter are statistically similar for both the buses. None of the pollutants except CO exceeded the TWA limits.