With cost often viewed as one of the major reasons to adopt open source technologies, the return on investment (ROI) of open source must be determined precisely when looking at deploying data integration solutions. This ROI Study looks in detail at all project costs: license (development, runtime, maintenance...), training and rampup, development and maintenance time, hardware and operating system, IT operations, etc. It also considers many intangible elements such as reliability, predictability, time to market. More than a theoretical report, the ROI Study provides not only hard numbers but also the tools IT organizations need to assess the return of investment of open source, and to compare this ROI with the one of alternative options: manual coding, and proprietary data integration solutions.