This research effort sought to examine the performance potential of a dual-expander cycle liquid oxygen-hydrogen engine with a conventional bell nozzle geometry. The analysis was performed using the NASA Numerical Propulsion System Simulation (NPSS) software to develop a full steady-state model of the engine concept. Validation for the theoretical engine model was completed using the same methodology to build a steady-state model of an RL10A-3-3A single expander cycle rocket engine with corroborating data from a similar modeling project performed at the NASA Glenn Research Center. Previous research performed at NASA and the Air Force Institute of Technology (AFIT) has identified the potential of dual-expander cycle technology to specifically improve the efficiency and capability of upper-stage liquid rocket engines. Dual-expander cycles also eliminate critical failure modes and design limitations present for single-expander cycle engines. This research seeks to identify potential LOX Expander Cycle (LEC) engine designs that exceed the performance of the current state of the art RL10B-2 engine flown on Centaur upper-stages. Results of this research found that the LEC engine concept achieved a 21.2% increase in engine thrust with a decrease in engine length and diameter of 52.0% and 15.8% respectively compared to the RL10B-2 engine. A 5.89% increase in vacuum specific impulse was also observed. The implications of these results could lead to significant launch cost savings and replacement of aging expander cycle technology in the rocket propulsion industry. In order to fully validate the results of this research, more knowledge is required regarding the heat transfer characteristics of supercritical oxygen for rocket thrust chamber cooling. Future work in this topic will focus on experimental LOX heat transfer research and model optimization to improve heat transfer estimations in the baseline model developed in this research and further explore the optimal performance potential and limitations of the LEC engine.