Continuous-mixture theory is based on the assumption that when a large number of components make up a mixture, the frequency distribution can be approximated by a continuous function. Here we apply this concept to multicomponent leaching or extraction from porous particles in a continuous-flow system. Desorption from the solid matrix and partitioning between the extraction fluid and an immiscible fluid in the pores of the matrix are included in the mathematical model. Intraparticle diffusion and external mass transfer are combined in a linear driving-force approximation. The mass balance equations for intraparticle and external fluid processes govern the time evolution of frequency distribution functions for different mixtures. The approach satisfactorily describes experimental data for supercritical extraction of triglycerides.