Knowledge of the elastic properties of a fluid is crucial for predicting its flow under high pressure, particularly in porous melt. However, when a fluid is confined to a nanopore, many of its thermodynamic properties change as compared to bulk. Here we study the effect,,o14.,. confinement on the bulk modulus of liquid argon adsorbed in mesopores using classical density functional theory. We show that, at pressures lower than the saturation pressure, high adsorption stress in the pore causesIth lowering of the fluid bulk modulus, a phenomenon which was recent] observed experimentally [Schappert, K.; Paster, R. Europhys. Lett. 2014, Os 5600]. Furthermore, we find that the pore size has a strong effect on the fluid bulk modulus, so that even at saturation, the elastic properties nanoconfined fluid differ from the bulk values. We show that this difference is also due to the adsorption stress. Our results provide',-a basis for 'a new : method for characterization of porous materials and have implications for such as coal or shale.