The transport sector needs to become sustainable and public transport has an important role to play. Green public procurement has proven to have great potential to influence the transition to a sustainable public transport sector. Sweden is a good example of a country that uses public procurement in the public transport sector to a large extent and has at the same time come far in the transition to renewable fuel. The aim of this study is to examine what role public transport authorities (PTAs) can have in supporting more environmentally sustainable public transport through public procurement. This was done by a content analysis regarding the expressions of environmental requirements historically, over a ten-year period, in tender documents in Sweden, followed by a workshop where the implications of the findings and future tender processes were discussed with relevant actors. The results showed that all the environmental requirements have become stricter during the studied period, but indicate a tendency for higher use of environmental requirements in tendering of larger areas as well as in tendering of public transport within cities. Specifically, for requirements for fuel, the same tenders also use specific requirements to a higher extent. However, the subsequent workshop discussions indicated that the use of specific requirements is one reason for disagreement among involved actors. Overall, this study of the Swedish public transport case showed that PTAs have a large potential to support more environmentally sustainable solutions using environmental requirements in public procurement.