We obtain the diffusion matrix, D, consisting of the main and cross-diffusion coefficients for a loaded AOT microemulsion, a quaternary system containing water (1)/AOT (2)/species (3)/octane (4). Here "species" is a component of the Belousov-Zhabotinsky reaction: NaBr, NaBrO3, bathoferroin, ferroin, or Br-2. The main and cross-diffusion coefficients of each species depend crucially on its solubility. For water-soluble species (the salts), D-13 and D-23 are large (much larger than the main diffusion coefficients) and positive. For species located mainly in the surfactant shell (bathoferroin or ferroin), D-13 and D-23 are large and negative. For oil-soluble Br-2, D-13 and D-23 are larger and more negative, whereas D-33 >> D-11, D-22. The coefficients D-31 and D-32 are small for all species studied.