Desquilbet and Bullock (2010) criticize some aspects of our analysis of the European Union’s (EU) spatial ex ante coexistence regulations (SEACERs) of genetically modified (GM) and non-GM crops presented in Demont et al. (2009). We argue that, besides misinterpreting some of our original arguments, the authors propose a policy analysis framework which is inconsistent with the main goal of the EU’s SEACERs. Their example incorrectly suggests that SEACERs play an additional role of regulating non-GM crop supply on
the market. This would be inefficient from a policy economics perspective, especially in an open economy
where global trade is taken into account. Therefore, we argue that analyzing flexibility of SEACERs in a market framework could lead to erroneous conclusions and in that case a simple farm level analysis such as presented in Demont et al. (2009) is preferred.