Adaptive modulation techniques (bit/power- loading) allow great optimisation of spectral efficiency, power consumption and error rates in wireless multicarrier systems. However, multicast transmissions complicate their implementation as there is no longer one single channel to optimize the transmission for. In this paper, a new approach to loading for OFDM on wireless multicast systems is proposed. We show that a great performance enhancement can be expected in ideal conditions. After deriving an upper bound for the error rate in these conditions, we study the performance degradation occurring with imperfect channel state information.