In scenarios where many receivers simultaneously are interested in the same data, multicast transmission is more bandwidth efficient than unicast. The reason is that the receivers of a multicast session share the resources through a common transmission tree. Since the resources are shared between the receivers, it is reasonable that the costs corresponding to these resources should be shared as well. This paper deals with fair cost sharing among multicast receivers. The work is based upon the assumption that costs should be shared based on resource usage. With this in mind, existing cost-allocation mechanisms are evaluated and the conclusion is that none of them is satisfactory fair. We therefore propose a new cost-allocation mechanism that allocates the costs according to the transmission path and obtained QoS level of each receiver.