Frontier-based exploration method are known to be efˇcient for multi-robot exploration systems. In this paper, we propose a novel, computationally inexpensive, frontier allocation method favoring a well balanced spatial distribution of robots in the environment. It is based on the computation of a position criteria. The position of a robot towards a frontier is deˇned by the number of robots closer to the frontier. Distances to frontiers are computed using a wavefront propagation from each frontier. The local minimum free potential ˇelds, thus created, are also used for navigation achieved by descending the potential ˇeld gradient. Comparisons with existing approaches in simulation demonstrated the efˇciency of our algorithm and experiments on robots validated the navigation method.