Performance enhancement of solid oxide fuel cell (SOFC) has been a very prominent research problem of the present era. One of the key performance-limiting factors is diffusional constraint encountered in SOFC cathodes during operation with air. While attempts at improving cell performance have been made through the optimization of geometries, flow rates, and operating conditions, very few studies have reported the potential for performance enhancement through the optimization of cathode gas composition. The present study takes an experimental as well as theoretical approach to examine the extent to which SOFC performance can be enhanced through alterations in the oxygen concentration of cathode gas (without varying the oxygen molar flow rate). An SOFC is operated for various cathodic oxygen concentrations, and the experimental protocol is simulated using a parametric computational fluid dynamics study. The results depict remarkable nonlinearities in the dependence of cell performance indicators on cathode gas oxygen concentration, which opens up a new dimension for the optimization of cell efficiency, contingent on the availability of oxygen, and the design and operational constraints unique to specific SOFC development ventures.