Bubbly liquid flow through fixed beds and its transition to dispersed-bubble flow is analyzed. The system is described as a compressible fluid filtrating through porous media. The system peculiarities-the isothermal variation of perfect gas in the spherical bubbles, weak compressibility of the liquid, etc.-are accounted for in the state equation for bubbly liquid. Dimensionless criteria were found determining the bubbly-liquid flow in packings at the macro (bed) scale as well as criterion for its stability at the micro (pore) scale. The modeling results are compared with the experimental data. (C) 2003 Elsevier Science Ltd. All rights reserved.