We consider an initial boundary value problem for a nonlinear differential system of two equations. Such a system is formed by the equations of compressible miscible flow in a one-dimensional porous medium. No assumption about the mobility ratio is involved. Under some reasonable assumptions on the data, we prove the existence of a global weak solution. Our basic approach is the semiGalerkin method. We use the technique of renormalized solutions for parabolic equations in the derivation of a priori estimates. Ž . Let T ) 0 and let ⍀ s 0, 1 . We set ⍀ s ⍀ = 0, T . We investigate T the following nonlinear initial boundary value problem of parabolic type in ⍀ :T