The hybrid use of off-site and on-site processes in construction projects has increased significantly over the past decade. The analysis and management of uncertainty in hybrid projects is not a trivial task as workflow variability in off-site and on-site operations can interact and amplify one another. The aim of this paper is to analyze various drivers of uncertainty such as high levels of project complexity, risk seeking behaviors, unavailability of resources, and combined variability in hybrid projects. Production data of two Australian construction companies were collected and utilized in modeling uncertainty. Findings show the significant effect of uncertainty drivers on project plan reliability and the necessity of an adequate uncertainty analysis and management in hybrid projects. The results of this study enhance the knowledge about management of hybrid projects and have the potential to improve the way construction companies deal with uncertainty in project environments.