In this paper we consider the issue of energy efficiency in random access networks and show that optimizing transmission probabilities of nodes can enhance network performance in terms of energy consumption and fairness. First, we propose a heuristic power control method that improves throughput, and then we model the Utility Constrained Energy Minimization (UCEM) problem in which the utility constraint takes into account single and multi node performance. UCEM is modeled as a convex optimization problem and Sequential Quadratic Programming (SQP) is used to achieve optimal transmission probabilities. Numerical results show that our method guarantees fairness, reduces energy consumption and enhances lifetime of such networks. Keywords-energy efficiency; slotted Aloha; utility function; convex optimization