Fluid properties of five binary mixtures relevant to shale gas and light tight oil in confined nano-channels are studied. Canonical (NVT) Monte Carlo simulations are used to determine internal energies of departure of pure fluids using the RASPA software system (Dubbeldam et al., 2015). The linear mixing rule proposed by Lucia et al. (2012) is used to determine internal energies of departure for mixtures, U-M(D), in confined spaces and compared to U-M(D) from direct NVT Monte Carlo simulation. The sensitivity of the mixture energy parameter, a(M), for the Gibbs-Helmholtz constrained (GHC) equation, confined fluid molar volume, V-M, and bubble point pressure are studied as a function of uncertainty in U-M(D). Results show that the sensitivity of confined fluid molar volume to 5% uncertainty in U-M(D) is less than 1% and that the GHC equation predicts physically meaningful reductions in bubble point pressure for light tight oils. (C) 2017 Elsevier Ltd. All rights reserved.