Gelatinization in excess of water and melting transition for different moisture contents of a ready-to-eat cereal formulation (RTE blend) and its major components, (i.e., oat flour, rice flour, and an oat-rice flour blend) were studied by differential scanning calorimetry (DSC) and rapid visco-analyzer (RVA). The highest swelling power was exhibited by the rice flour and the lowest by the RTE blend. Two endothermic peaks under excess of water were exhibited by all materials, at 53-75°C and 80-102°C, and they were associated to gelatinization and cereal protein denaturation, respectively. A third peak appearing in all materials except in rice flour, at higher temperatures (102-116°C), was attributed to the melting of the amylose-lipid complexes. The effect of water in the melting of the flours and blends was well described by the Flory-Huggins equation and its parameters agreed well with those reported in the literature for starchy products. A theoretical value of the polymer-diluent (starchwater) interaction factor for starch of 0.36 was calculated from a combined model of Hildebrand empirical approach to solubility and the Flory-Huggins theory, and reasonably compared with the interaction parameter (χ) obtained for the materials considered in this work. State diagrams for the oat-rice flour blend and for the RTE blend going through an extrusion process were finally obtained.