We present values of the self-diffusion coefficients at 25 degrees C of four hydrocarbons (n-pentane, n-hexane, cyclohexane, and o-xylene) at saturation concentrations in (heavy) water. To calculate the corresponding values for the series of n-alkanes, we suggest two alternative scaling relations for the dependence of the self-diffusion coefficients on the molecular weights of the n-alkanes. The scaling relations are "calibrated" using the value presented for n-pentane.