<p>Studies on hot-firing tests for designing methane-fueled ribbed combustion chambers are scarce. Therefore, in this study, a comparative analysis of heat flux variations in liquid-oxygen/gaseous-methane ribbed combustion chambers with different rib configurations was performed to assess the effect of the rib configuration on thermal performance. Four combustion chambers—one machined chamber (smooth wall) and three additively manufactured chambers (smooth wall, uncooled ribs, and cooled ribs)—were subjected to cold-flow and hot-firing tests using the same injector head and nozzle. In the cold-flow tests, the additively manufactured chambers, with coarser surfaces, exhibited a higher pressure loss than the machined chamber, with smoother surfaces; this validated the predictive accuracy of the equivalent wall roughness considering actual friction coefficients. Additionally, the heat-flux increments and rib efficiencies were investigated, revealing distinct thermal behaviors in the chamber and nozzle areas. The chamber with uncooled ribs exhibited heat flux increases roughly proportional to the increase in surface area, while the chamber with cooled ribs exhibited a significantly higher heat flux, which is attributed to modifications in the geometry and alignment of the cooling channels. Meanwhile, both ribbed chambers exhibited a lower heat flux in the nozzle than their smooth-walled counterparts. The results of this study can help improve the thermal management and efficiency of rocket engines.</p>