Electron drift, Hall mobility and thermoelectric power in InP xAs1-x, GaxIn1-xAs and InAs xSb1-x have been calculated by an iterative solution of the Boltzmann equation. A Kane-type band structure corrected for the lattice disorder is assumed. All the relevant scattering mechanisms are included together with band non-parabolicity, wavefunction admixture, degeneracy of the distribution function and screening of the scattering probabilities due to free carriers. Only the ionised impurity concentration (Ni) and the alloy scattering potential ( Delta Ea) have been treated as adjustable parameters to be determined from a fit with the experimental data. Variations of the other different material parameters across the alloy system have been taken from different sources, or reasonable assumptions are made regarding such variations. A large number of experimental results on both mobility and thermoelectric power are considered and good agreement is obtained with Delta Ea larger than that given by the difference in electron affinity between the constituent compounds.