In this paper, we define and validate a new multidimensional measure of Open Source Software (OSS) project survivability, called Project Viability. Project viability has three dimensions: vigor, resilience, and organization. We define each of these dimensions and formulate an index called the Viability Index (VI) to combine all three dimensions. Archival data of projects hosted at SourceForge.net are used for the empirical validation of the measure. An Analysis Sample (n=136) is used to assign weights to each dimension of project viability and to determine a suitable cut-off point for VI. Cross-validation of the measure is performed on a hold-out Validation Sample (n=96). We demonstrate that project viability is a robust and valid measure of OSS project survivability that can be used to predict the failure or survival of an OSS project accurately. It is a tangible measure that can be used by organizations to compare various OSS projects and to make informed decisions regarding investment in the OSS domain.