The theory and experimentation reported are for the purpose of determining the effect of particle size proportions in soils on their maximum bulk densities and other properties affected by compaction. If the different size classes in a bidisperse or tridisperse mixture have very large effective diameter ratios and if certain other simplifying requirements are followed, it is shown theoretically that the minimum bulk volume of the mixtures can be predicted from the volume proportions of the different-sized particles present. The minimum bulk volumes and hence maximum bulk densities of two prepared textural sequences, Stockton silty clay and Monterey sand mixtures, were obtained after kneading compaction at different water contents and were examined with respect to the above theory. The relationships between water content and compacted bulk density, between water content and suction of compacted soils, and the formally calculated mean effective pore diameter distribution at minimum and maximum bulk density are presented and discussed.