In this paper, an opportunistic cooperative ad hoc sensor network with randomly located nodes is analyzed. The randomness of nodes' locations is captured by a homogeneous Poisson point process. The effect of imperfect interference cancellation is also taken into account in the analysis. Based on the theory of stochastic geometry, outage probability and cooperative gain are derived. It is demonstrated that explicit performance gain can be achieved through cooperation. The analyses are corroborated by extensive simulation results and the analytical results can thus serve as a guideline for wireless sensor network design.