Unconventional sandstone reservoirs with ultralow permeability (1 mD < K-air < 10 mD, where K-air, represents the permeability in air) and superlow permeability (0.1 mD < K-air < 1 mD) in China are widely distributed in major basins and have significant economic potential. (Here, D is a permeability unit: 1D = 1000mD = 1 mu m(2)) A comparative study has been, performed here on three Upper Triassic sandstone reservoirs with superlow permeability in the southern Ordos Basin to understand,the characteristics of each reservoir, the differences in reservoir porosity and permeability, and their causes. The study shows that pore type is the main factor that controls the physical property of nonfractured, superlow permeability sandstone reservoirs in the area of study. The main pore type observed in all three reservoirs is dissolution-enhanced intergranular, which comprises a maximum of 70% of the total porosity. Remnant intergranular and intragranular dissolution pores are also observed in these reservoirs. The pore throat size of dissolution-enhanced intergranular pores is generally 2-3 times larger than that of the intragrantilar dissolution type. Therefore, the reservoir with the greatest quantity of dissolution-enhanced intergranular pores has a poorer sorting of, ore throat sizes and stronger microscopic heterogeneity. The dissolution-enchariced intergranular pores, on the other hand, also contribute to higher surface porosity, larger average pore diameter, higher pore throat coordination value; and, most importantly, higher permeability. This latter result contrasts with observations of conventional sandstone reservoirs, hi which better pore throat sorting is favored for permeability.