Within the framework of a study on the properties of carbon nanotubes, a promising new material, we performed numerical simulation of hydrogen adsorption at room temperature in single-walled nanotubes. The structure of this material is favorable to the adsorption phenomenon because of the narrow size distribution of the nanotube diameters, which have dimensions on the order of the range of the carbon attractive interaction. We discuss the influence of the single-walled carbon nanotube diameters on the relative arrangement of carbon atoms and hydrogen molecules within an array of parallel single-walled carbon nanotubes. We also studied the influence on adsorption of the distance between the nearest-neighbor nanotubes.