The use of Commercial-off-the-Shelf (COTS) software has become more and more important in state-of-the-art and state-of-the-practice software and system development. The use of COTS software promises faster time-to-market, reduced development cost, increased productivity, and the possibility for companies to focus on their own core competencies. At the same time COTS software raises risks such as economic instability of the COTS software vendor, unknown quality properties of the COTS software in use, and side effects of the COTS software on the final product. Typically, COTS-based development - in parallel to the traditional development cycle, e.g. waterfall, spiral - consists of four phases. The first phase - COTS assessment and selection - is the most crucial phase in the COTS-based cycle since long-term decisions on which COTS software will be used in a software system are made here. A late recognition that the "wrong" COTS software was used can become extremely costly for a software organization. This paper presents a repeatable, cost-efficient, and systematic method for performing measurement-based COTS assessment and selection. Moreover, cost/benefit analysis results of two industrial pilot projects, in which the method was successfully applied, are presented.