Pore-throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale That continuum is. documented in this article using previously published data on the pore and pore-throat sizes of conventional reservoir rocks, tight-gas sandstones, and shales. For measures of central tendency (mean, mode, median), pore-throat sizes (diameters) are generally greater than 2 mu m in conventional reservoir rocks, range from about 2 to 0.03 mu m in tight-gas sandstones, and range from 0.1 to 0.005 mu m in shales. Hydrocarbon molecules, anasphaltenes, ring structures, paraffins, and methane, form another continuum, ranging from 100 angstrom (0.01 mu m) for asphaltenes to 3.8 angstrom (0.00038 mu m) for methane. The pore-throat size continuum provides a useful perspective for considering (1) the emplacement of petroleum in consolidated siliciclastics and (2) fluid flow through fine-grained source rocks now being exploited as reservoirs.