This annotated slide presentation explores the importance of considering power system “operational constraints” when conducting production cost modeling to explore the potential value of making new “flexibility investments,” such as new natural gas combustion turbines, new inter-regional transmission lines or new battery energy storage systems. We used a power system “production cost” model (Power System Optimization) and an IEEE industry test power system topology (IEEE RTS 96 test system, updated by NREL for the GLMC), to model four different illustrative power system scenarios to explore the potential importance of incorporating operational constraints in production cost modeling. These scenarios include: (i) A Baseline which closely follows the original IEEE test system; (ii) A High Variable Renewable Energy (VRE) scenario that includes three times the amount of renewable generation as the Baseline; (iii) a Flexible Natural Gas scenario that explores system operations with twice the amount of flexible natural gas generation as the Baseline; and (iv) An Energy Storage scenario that includes the addition of 1 GW of battery energy storage to the Baseline system. The power system modeling done for this project strongly suggests that estimates of system operating cost, power prices, and dispatch patterns differ substantially depending on if operational constraints are explicitly considered in the production cost modeling of the scenarios.