Abstract We address the problem of optimal path ?nding for multiple agents where agents must not collide and their total travel cost should be minimized. Previous work used traditional single-agent search variants of the A* algorithm. We present a novel formalization for this problem which includes a search tree called the increasing cost tree (ICT) and a corresponding search algorithm that ?nds optimal solutions. We analyze this new formalization and compare it to the previous state-of-the-ar A*-based approach. Experimental results on various domains show the bene?ts and drawbacks of this approach. A speedup of up to 3 orders of magnitude was obtained in a number of cases.