This study tests hypotheses about behavioural spillover in the environmental domain as well as the impacts of monetary inducements and verbal praise on behavioural spillover by means of a field experiment. A sample of 194 students from a large university in Denmark were randomly allocated to a control group or to one of two experimental conditions where they were encouraged to purchase “green” products by means of either financial compensation and incentives or verbal encouragement and praise. Participants answered a baseline survey containing questions concerning a wide range of environmentally relevant behaviours and after a six weeks intervention period where they were requested to keep track of their purchases by means of a shopping diary they answered a second survey with the same content as the first. This allowed us to analyse the change in self-reported pro-environmental behaviours over the six weeks, to identify instances of behavioural spillover from “green” purchase behaviour to other pro-environmental behaviours and to investigate if such spillover was affected by the nature of the intervention. The study revealed a positive spillover from “green” purchasing to other pro-environmental behaviours. However, the spillover mostly affects low-cost behaviours. Not unexpectedly, the monetary inducement had a stronger direct impact on “green” shopping than verbal encouragement and praise. However, contrary to popular beliefs, the spillover effects of a monetary inducement on other pro-environmental behaviours are at least as strong as that of verbal encouragement and praise.