In 1998, Genetically Modified (GM) maize entered European Agriculture. After the publication of the European Commission's guidelines on coexistence in 2003, Portugal developed ex-ante regulatory and ex-post tort liability rules on the coexistence of GM and non-GM maize crops. There is an on-going debate on the extent to which the coexistence policies affect adoption. In this study we measure the costs and benefits of planting GM maize as a member of a cooperative. All group members achieved a higher gross margin by planting GM maize rather than non-GM maize on their farms. Group members did not face any ex-post liability costs and had zero ex-ante regulatory costs as they could easily internalize the ex-ante coexistence regulations. The results show that coexistence regulations such as informing neighbors or keeping minimum distances do not necessarily lead to increased production costs provided they are flexible enough.