The binary diffusion coefficients of CO2 in tetradecane were measured at 311 K and 1.905 MPa by dissolution of CO2 in liquid tetradecane. On the basis of the constant diffusivity diffusion theory of Reamer et al., the diffusion coefficients were first obtained from the injected CO2 volume vs time data and the solubility of CO2 in liquid tetradecane. An uncertainty function Ft, similar to the data analysis of of Liu et al. for uptake curves of gases in zeolite, was introduced to describe the diffusion process, and a linear relationship has been deduced for the evaluation of the diffusion coefficients at different diffusion times from the dissolution data. The diffusivity variation during the diffusion process can be represented by a concentration/time-dependent diffusivity D-tau. The applicability of the new method has been tested in the binary diffusion of the CO2-tetradecane system measured in this work. and for the diffusion data of the methane-hydrocarbon systems of Reamer et al. The concentration-dependent diffusion coefficients obtained were compared with the existing diffusion coefficient data.