Frontier-based exploration methods are efficient for multi-robot exploration systems. In this paper, enhanced frontier-based techniques are used with team of cooperating mobile robots to explore unknown environment. The aim of the exploration algorithm is to minimize the exploration time by coordinating the robots to maximize overall utility by minimizing the potential of overlapping in information gained amongst the robots. The proposed frontier-based exploration algorithm is based on a new bidding function to decrease the overlap between the robots in addition to the utility and cost parameters. A special parameter depends on the future positions of the robots is also considered. The proposed algorithm has been tested with different environments. We also compared it to A* algorithm. Comparisons demonstrated the efficiency of proposed algorithm.