The performance of any multiuser wireless communications system is strongly affected by interference. Consequently, the design of such systems must comply with some outage probability criteria. Although interference occurs in a mutual entangled basis, with wireless devices interfering with each other, outage is commonly considered on an individual per-device basis. This approach, however, is a simplified solution to a more intricate multidimensional and system-wide problem, in which several mutually interfering devices may be experiencing an outage simultaneously. The true outage probability across several devices is given by a set of mutual entangled boundary conditions to be fulfilled. This paper presents useful novel formulations for outage probability in multiuser wireless settings, here named mutual outage probability (MOP), for the interference-limited environment. Several scenarios are envisaged, in which some signals are in outage, whereas others are not and still for some others these conditions are irrelevant, all at the same time. We introduce a general framework for calculating the MOP, and present closed-form formulas for the Rayleigh case. Finally, we illustrate the practical use of these formulations in a call admission control application.