Accurate knowledge of the compositions of the equilibrium phases in the systems containing gas hydrates is essential for many hydrate-based separation processes. Unfortunately, there are limited sets of such experimental data available in the literature partly due to the difficulties in measurements of the compositions of the phases in equilibrium with gas hydrate. Consequently, satisfactory accuracy of the measurements may not be obvious. Therefore, reliability of the corresponding data should be checked prior to their further applications. In this article, we present a thermodynamic assessment test (consistency test) based on the area test approach for the experimental compositional data of vapor phase in equilibrium with gas hydrate + liquid water for the carbon dioxide + methane or nitrogen + water system. The van der Waals and Platteeuw (vdW-P) solid solution theory is used to model the hydrate phase, and the Valderrama-Patel-Teja equation of state (VPT-EoS) along with the nondensity dependent (NDD) mixing rule is applied to deal with the fluid phases. The results show that only one of the studied experimental data sets seems to be thermodynamically consistent, and the rest of the data seem to be either not fully consistent or inconsistent.