Self-diffusion coefficients have been measured in homogeneous mixtures of methane + hexane, ethane + hexane, methane + octane, ethane + octan, methane + decane, ethane + decane, and methane + hexane + benzene over the whole concentration range, at 303.2 K and 333.2 K and 30 MPa, 40 MPa, and 50 MPa. The experiments were performed in a glass cell by application of the NMR-PGSE technique. The estimated accuracy of the measurements is +/-5%. Experimental self-diffusion coefficients were compared to the Sigmund correlation, which was found not to fit the experimental data.