Today, more than 85% of firms engaged in high levels of model-based engineering and construction have a positive perception of the value they receive for the time, money, and efforts they have expended on their modeling programs. Nevertheless, there are no established processes and metrics for measuring the progress of a model-driven engineering process, as particularly the deliverable type, schedule reporting, and their impacts have changed. A key underlying challenge is how progress and level of effort in a model-driven engineering process can be measured and reported. Definitions such as level of development (LOD) have been established in the commercial building sector for tracking completeness in modeling work, yet there are no established processes and metrics that can reliably measure the progress of a model-driven engineering process as a function of the maturity of the model and the data that supports the engineering process. To address this gap in knowledge, this paper presents a new framework based on a new set of model maturity index (MMI) definitions that measures maturity and progress in engineering work; based on factors that provide insight, manage, control opportunities, and accounts for the unavailability of vendor data, design changes, re-work and design development, model review comments, operability reviews, hazard and operability studies, among other factors. The MMI definitions were validated via charrettes with engineering and project controls experts from the process industrial sector.