National audience The purpose of the article is to evaluate the EU Directive on CO2 emission allowances carried out using the GEMINI-E3 model. After a brief reminder of the EU Directive and a description of the model, scenarios corresponding to different possible allocation rules are described and analysed. If the European allowance mechanism creates a unified market for eligible companies, it can at the same time distort other sectors of activity in each country. This results in a single carbon price for all eligible companies, but a different carbon price for other sectors, also different from one country to another, leading to potentially significant additional costs.