Non-gray radiation occurs in high temperature condition with participating gases, such as water vapor and carbon dioxide in combustion products. Spectral-line-based weighted-sum-of-gray-gases (SLW) method is widely used to model the non-gray radiative properties to obtain the overall radiative heat source and heat flux, while the contribution of each gray gas is usually not investigated. Knowledge of these contributions can provide information on how to optimize the SLW method or combine different radiative transfer equation solvers for different gray gases to save computational time. SLW method is used here to investigate its gray gas contribution and corresponding accuracies of the finite volume and P1 method in these gray gases. Monte Carlo method is used for each gray gas to serve as reference solution. Gray gas contributions to the total heat source and heat flux for three cases are analyzed in detail. Results show that different gray gases have completely different contributions and finite volume method and P1 method have different accuracies for the gray gases. (C) 2018 Elsevier Ltd. All rights reserved.