Abstract.Given a graph T , define the group Fr to be that generated by the vertices of T, with a defining relation xy -yx for each pair x, y of adjacent vertices of T. In this article, we examine the groups Fr-, where the graph T is an H-gon, (n > 4). We use a covering space argument to prove that in this case, the commutator subgroup Ff contains the fundamental group of the orientable surface of genus 1 + (n -4)2"-3 . We then use this result to classify all finite graphs T for which Fp is a free group.To each graph T = ( V, E), with vertex set V and edge set E, we associate a presentation PT whose generators are the elements of V, and whose relations are {xy = yx\x ,y adjacent vertices of T).