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, NaBrO(3), 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.