The accurate modelling of confined fluids has a significant impact in the design of new processes and technologies. This work aims to provide new tools for the description of the adsorption of fluids in nanoporous solid materials. In terms of theoretical modelling, an extension of the statistical associating fluid theory (in its SAFT-VR-Mie version) equation of state is developed to take into account the effect of confinement of fluids into cylindrical pores. The capability of the proposed model is showcased by fitting adsorption isotherms of pure fluids such as; methane and n−nonane on activated carbons; ethane, n−hexane and benzene on MCM- 41, and methane and carbon dioxide on carbon surrogate models of shale rocks; providing for an accurate correlation of the data with parameters that are temperature- independent and robust. Further insight is obtained through molecular simulation of model systems, where the onus is on studying the effect of molecular and pore morphologies on adsorption isotherms and diffusion. Three distinct geometries of fluids are considered; trimers forming a flexible chain, a rigid linear chain, and a ring-like structure (triangular configuration). Moreover, cylindrical pores with three different values of pore diameters and three levels of solid-fluid interaction strength are employed. It is seen that both the molecular shape and the surface attractions play a decisive role in the shape of the adsorption isotherm. In general, the ring molecules show a larger adsorption, while the fully flexible model shows the smallest adsorption. High adsorption and diffusion are observed for the linear stiff molecules in ultra-confinement, due to a phase transition of the adsorbed fluid into a nematic liquid crystal. A further study is presented about the effect that pore geometry has on adsorption isotherms, where the chosen pores have cross sections representing: triangle, square, pentagon, hexagon, octagon, decagon and circle configurations (all of them with the same cross-sectional area). For high fluid-solid energy interactions and, in particular, for pores of dimensions commensurate with the molecular size, the presence of vertices in the pores and the intensity of the energy on these areas significantly enhance the adsorption of fluids.