This paper studies the performance of Mobile Ad hoc Networks (MANETs) when the nodes, that form a Poisson point process, selfishly choose their Medium Access Probability (MAP). We consider goodput and delay as the performance metric that each node is interested in opt imizing taking into account the transmission energy costs. We introduce a pricing scheme based on the transmissi on energy requirements and compute the symmetric Nash equilibria of the game in closed form. It is shown that by appropriately pricing the nodes, the selfish behavior of the nodes can be used to achieve the social optimum at equil ibrium. The Price of Anarchy is then analyzed for these games. For the game with delay based utility, we bound t he price of anarchy and study the effect of the price factor. For the game with goodput based utility, it is shown t hat price of anarchy is infinite at the price factor that achieves the global optima.