There is potential for over-provision of environmental harms and under-provision of environmental benefits associated with GM crops. As a result, strong public regulation is needed to ensure that full social values are considered. However, one reason for opposition to GM crops is a lack of public trust in regulatory institutions and science, and the limited opportunities afforded to public-participation and nonscientific concerns. We aim to demonstrate the trade-off between social cost and managing the risks of gene flow arising from environmental release of GM canola in Australia, using the framework of a probabilistic risk assessment and safety-rule decision mechanism.