A robust, simple methodology for analysis of isotherms for the adsorption of fluids above their critical temperature onto nanostructured materials is presented. The analysis of hydrogen adsorption in a metal-organic framework is used as an example to illustrate the methodology, which allows the estimation of the absolute adsorption into nanoporous systems. Further advantages of employing this analysis are that adsorption systems can be described using a small number of parameters, and that excess and absolute isotherms can be extrapolated and used to predict adsorption behaviour at higher pressures and over different temperature ranges. Thermodynamic calculations, using the exact Clapeyron equation and the Clausius-Clapeyron approximation applied to the example dataset, are presented and compared. Conventional compression of hydrogen and adsorptive storage are evaluated, with an illustration of the pressure ranges in which adsorption facilitates storage of greater volumes of hydrogen than normal compression in the same operating conditions.