Powder X-ray diffraction studies of solid state reactions in the La2O3-Ga2O3-MoO3 system, as well as a critical assessment of the previously published diffraction, thermal analysis and conductivity data on the compound La3GaMo2O12, reported to form from stoichiometric quantities of La2O3, Ga2O3 and MoO3, show that this material is in fact a mixture of four known binary/ternary metal oxides. Quantitative analysis by Rietveld refinements of diffraction data suggests that the first product formed in this system on heating is La2Mo2O9, followed by La2MoO6 and finally LaGaO3. On heating beyond 1000 degrees C, the amounts of La2Mo2O9 and LaGaO3 grow at the expense of La2MoO6 and Ga2O3. (c) 2007 Elsevier B.V. All rights reserved.