Being able to provide high-quality, metro-like transit service at a fraction of the cost of other options, bus rapid transit (BRT) has been viewed as one of the most cost-effective public mass transport systems suitable for urban areas. Considering significant amounts of greenhouse gas (GHG) and air pollutant emissions are attributed to the transport sector, deploying low carbon buses for BRT systems should be of high priority. With a view to promoting low carbon buses instead of diesel buses for a BRT system currently being planned in Amman, Jordan, this paper evaluates several low carbon bus options – hybrid, plug-in hybrid, opportunity charging, trolleybus, and battery electric bus options – against the baseline case of diesel buses. While low carbon buses reduce GHG and air pollutant emissions often considerably, they usually require higher upfront capital costs and additional infrastructure investments. On the other hand, they tend to incur lower energy and maintenance costs and have a longer lifetime particularly for battery electric buses. All these advantages and disadvantages are included in the assessment of low carbon bus options relative to diesel buses. For the trunk routes of the Amman BRT, the analysis shows that the opportunity charging bus can be the most appealing option having a positive internal rate of return (IRR) for the incremental investment costs. For the feeder routes, both low carbon bus options considered, hybrid and battery electric, do not result in a positive IRR. Nevertheless, the battery electric bus is found to be a comparatively better option than the hybrid bus. In consideration of variability in several parameters used in the analysis such as capital expenditures, electricity price, and diesel price, a sensitivity analysis is conducted for both trunk and feeder routes. The results show that IRR could increase favorably under certain conditions.