Isothermal diffusion coefficients are measured in binary and ternary liquid mixtures by the open ended capillary technique. The technique has been validated by reproducing literature data on water-ethanol binary systems. It has also been used to study the composition dependence of the diffusion coefficients in the binary and ternary systems obtained with the tetrahydronaphtalene, isobutyl benzene, and dodecane organic compounds, with the ternary one being a model system of crude oil. Difficulties related to a new procedure to interpret the experimental results at short times are presented.