Scarce bandwidth and interferences in mobile ad-hoc networks yield the need for more efficient flooding techniques than these used on usual wired networks. In this paper, we compare some new flooding mechanisms that were proposed. We namely present multi-point relay (MPR) flooding and gateway flooding. We investigate the matter theoretically via mathematical modelling, as well as practically via simulations. It is shown that when the network is dense, more than 2/3 of the gateway nodes participate in the retransmissions, while on the other hand the density of multi-point relay retransmitters is 1/nu , where nu is the node density.