We have utilized the Taylor dispersion technique to measure the infinite dilution mutual diffusion coefficients of 1-octene and 1-tetradecene in subcritical and supercritical ethane and in subcritical propane in the temperature range 293.15-338.15 K and the pressure range 5.52-11.03 MPa. For ethane, the measurements were done on either side of the critical temperature with the pressure above the critical pressure.