This paper provided and overview of the state-of-the-art research in the area of COTS- based software systems reliability analysis. First, various definitions for COTS and reliability are presented. Then, the paper presents reliability analysis for COTS-based software applications. The benefit of COTS-based software application is evident in the software system. However, many questions related to the COTS-based software systems are still unanswered. In further, to evaluation the overall application reliability existing work take some important considerations are reliability of COTS component, COTS components’ operational profile and operational profiles of COTS-based software systems.