Probabilistic rewards increase the use of reusable cups

•Single-use disposable cups cause pollution and release microplastics.•Reusable cups are an eco-friendlier and healthier alternative.•Probabilistic rewards (5 % chance to win a $5 gift card) increase reusable cup use.•Probabilistic rewards (10 % chance to win a free coffee) have similar effects.•Probabilistic rewards are a promising intervention to promote reusables. Given the environmental threat posed by single-use disposable cups, increasing the use of reusable cups among consumers is vital. To achieve this goal, the current study examined how probabilistic rewards influenced the use of reusable cups at cafés on a university campus. In the pilot study, customers with reusable cups were offered a 5 % chance to win a $5 gift card. This probabilistic reward produced a significant increase in the use of reusable cups compared to baseline. In a separate field experiment, one café offered customers with reusable cups a 10 % chance to win a free coffee, while another café served as a control site without the reward. The probabilistic reward led to a significant increase in the use of reusable cups. Together, these findings provide initial support for the implementation of probabilistic rewards to increase the use of reusable cups, with empirical, theoretical, and practical implications for sustainable consumption.