Mobile software systems are characterized by their highly dynamic and unpredictable execution context. Such systems are permeating a number of domains where the systems operate in constantly changing conditions. We refer to such systems as Situated Software Systems. These systems are often deployed in mission-critical settings with stringent reliability requirements. Existing approaches to performing reliability analysis are insufficient in meeting the demands of situated software systems. We propose an approach aimed at such systems and present it in the form of a framework and tool suite known as REsilient SItuated SofTware system (RESIST). The framework utilizes information from the system's context to produce reliability predictions, and places the system in the optimally reliable configuration with respect to other competing quality attributes. Keywords-Context Awareness; Software Architecture; SelfAdaptive Systems; Service-Oriented Architecture; Mobility