This study models the CO2 emissions from electric (EV) and plug-in hybrid electric vehicles (PHEV), and compares the results to published values for the CO2 emissions from conventional vehicles based on internal combustion engines (ICE). PHEVs require fewer batteries than EVs which can make them lighter and more efficient than EVs. PHEVs can also operate their onboard ICEs more efficiently than can conventional vehicles. From this, it was theorized that PHEVs may be able to emit less CO2 than both conventional vehicles and EVs given certain power generation mixes of varying CO2 intensities. Amongst the results it was shown that with a highly CO2 intensive power generation mix, such as in China, PHEVs had the potential to be responsible for fewer tank to wheel CO2 emissions over their entire range than both a similar electric and conventional vehicle. The results also showed that unless highly CO2 intensive countries pursue a major decarbonization of their power generation, they will not be able to fully take advantage of the ability of EVs and PHEVs to reduce the CO2 emissions from automotive transport.