Abstract: The behaviour of bifurcations for thermal convectional flow in porous media, with respect to two parameters: bifurcational Rayleigh number and auxiliary aspect ratio of rectangular porous media, is studied. Attention is focused on those values of the aspect ratio at which, the two lowest critical Rayleigh numbers are near each other. We found the secondary bifurcation of the thermal convectional flow by means of the Liapunov-Schmidt reduction, and give the asymptotical expansions of the primary and secondar...