We report the Fickian diffusion coefficients in 20 ternary mixtures formed by 1,2,3,4-tetrahydronaphthalene (THN), isobutylbenzene (IBB) and n-dodecane (nC12) measured by, the Taylor dispersion technique at 298.1 K and atmospheric pressure. Four,diffusion-coefficients of the ternary mixtures were measured along six concentration paths starting on one binary subsystem and moving toward the other one;, We found expressions for the diffusion matrix of a ternary mixture approaching: to the binary limits. The measured diffusion coefficients were thoroughly Verified by comparison with the theoretical asymptotic behavior. The main diffusion coefficients vary smoothly over the entire concentration space and D-11 is always larger than D-22. One of the two cross diffusion coefficients is of the same order of magnitude as the main ones and, hence, not negligible, whereas the other-one is close to zero. The investigated mixtures-also comprise compositions that were examined in microgravity experiments in the ESA DCMIX1 project.