In this paper we propose a completely distributed multi-robot coordination algorithm to explore and map terrain. This algorithm is based on a market bidding process of unrevealed frontiers, where the bids are calculated by each robot. When it reaches the target the robot makes a decision by itself, which involves every one of the team members without lost of time in a distributed behavior and without the necessity of a central module. The result is an efficient and fault tolerant approach. The bid function includes the distance of the actual robot towards the frontier, the distances to the others robots and theirs objectives. This function gives a tendency of robots separation in a minimum route towards the frontier.