The NpT + test-particle method for the calculation of vapor-liquid equilibria by molecular simulations is extended to ternary mixtures. It is applied to the system methane + ethane + carbon dioxide, for which all binary molecular interaction models are available from previous work. Methane is described as one-center Lennard-Jones fluid, ethane as two-center Lennard-Jones flui, and carbon dioxie as two-center Lennard-Jones plus point quadrupole fluid. The unlike interactions are treated in the same way as the binary mixtures, using two parameters for each binary interaction. No ternary parameters are introduced. Vapor-liquid phase equilibria are calculated for the ternary mixture at the following temperature-pressure pairs : 233.15 K-2 MPa; 250.5 K-2 MPa; and 250.5 K-3.04 MPa. Comparison of the simulation data with experimental and equation-of-state results shows excellent agreement. Bubble and dew densities are also reported.