When National Airspace System (NAS) flight demand (e.g., Flight Operator operations) exceeds capacity (e.g., airport-, weather-, airspace-related) at a NAS resource the result is delay. To ensure an efficient NAS, the Federal Aviation Administration (FAA) uses various Time-Based Management (TBM) capabilities to balance capacity and demand across NAS resources. These capabilities assign the resulting delay across the resource flight demand. For example, the FAA uses the Time-Based Flow Management (TBFM) system to manage the balance between demand and capacity at arrival airports and departure fixes/flows by assigning delays across airborne and ground-based flights. TBFM is not creating delay, rather assigning delay that exists within the NAS to balance traffic demand with available capacity. TBFM uses controlled departure times to assign this delay on an as-requested approach. There is a desire among flight operators to provide priority inputs that can be accounted for by TBFM in order to minimize delay assigned to those flights that are most important to them in meeting their business objectives. Fleet Prioritization concepts, which intend to address this desire to better accommodate flight operator preferences as part of TBM, is considered consistent with achieving increased Operational Flexibility, one of four stated objectives in the FAA’s Vision for Trajectory-Based Operations (TBO).The MITRE Corporation in collaboration with the Federal Aviation Administration (FAA) is analyzing and exploring how a TBM Fleet Prioritization Service can be incorporated as part of future TBFM system capabilities. The Flight Operators’ needs for Fleet Prioritization and a concept for this was investigated, including concept elements that would be needed. Process-, procedural-, and automation-based methods were identified to achieve Fleet Prioritization goals. The scope of shortfalls related to TBFM and broader TBM operations were explored and data analysis performed to determine to what extent operational and/or business considerations necessitate the prioritization of flights to reallocate assigned delay in TBM operations. TBM assigned departure delays can vary widely for a flight; however, current operational TBM practices provide only a limited planning horizon for potential prioritization activities. The prioritization of flights requires sufficient planning time to ensure that the flight operators can meet business needs. Further data analysis highlighted that the advantages of applying increased scheduling lead-time as a means to minimize delay are location-dependent and not consistent NAS-wide. Therefore, any envisioned Fleet Prioritization service will require location-specific considerations. This paper will describe how the FAA should make both near-term and longer-term improvements to exchange data with flight operators, mature the concept, and utilize existing capabilities to improve flight operator preference accommodation.