Public transport can represent an important solution to decarbonize the sector, even more when relying on low-carbon powertrains. This work will focus on two promising options for urban mobility, comparing the CO2 emissions intensity of battery electric buses and biomethane-powered internal combustion engines. The comparison is performed on a well-to-wheels basis, to account for the entire supply chain that is of particular importance for these two solutions, as most of the emissions occurs in the well-to-tank phase. The outcome of the study confirms that interesting emissions savings can be achieved through the substitution of diesel buses with these low-carbon alternatives. These values confirm the interesting opportunity represented by these technologies compared to the current situation, and even more when considering them against the use of private cars.