Transit operators are gradually incorporating hybrid and electric vehicles in existing onventional-drive and natural gas fleets, in an effort to improve carbon-footprint of transit services. Naturally, there are significant trade-offs in terms of purchase, operation and management costs between the various propulsion systems, which complicate fleet replacement and vehicle purchase decisions for agencies. To that end, the objective of this study is to provide an ex-ante evaluation of bus fleet management plans in cases of fleets with mixed propulsion technologies. An integer programming model is exploited for that purpose, seeking to minimize the total cost of purchasing, operating and selling buses, under various fiscal and operational constraints. A realistic data set from various sources is collected and a thorough scenario analysis is performed to assess the various trade-offs between different propulsion technologies. Results show that the largest reduction in the fleet management cost stems from favorable conditions for the purchase of more fuel-efficient types of buses, such as electric and natural gas buses.