Compared with previous reforms, the main innovation of the 2003 CAP reform is the inclusion of the single payment system: the main principle is to break the link between support to farm incomes and the act of agricultural production. However, this reform allows exemptions to this principle at the Member States’ discretion. The objective of this article is to assess the consequences of the four implementation options of this new system on markets and incomes at the French level. Simulations show that unlike farm incomes, impacts on agricultural markets are relatively insensitive to these options. According to our simulations, the opportunity of introducing a single aid to forage areas instead of animal direct aid appears to be a possible compromise between the various stakes.