The chemical transport reaction method (CTR) is very convenient for the preparation of well defined samples for physical investigations and for materials research even if several solid phases may coesist in the system or a phase with homogeneity range appears. The very important question concerning the kind and composition of the deposited phase can be answered by a thermodynamics analysis. The steady-state model proposed by the authors includes the concept of equal component activities of source and sink as a special case, in other cases the flux function methodology no longer becomes consistent with a steady-state flux. The limitations of the different models are discussed. The conclusions are compared with experimental results.