The vapor-liquid equilibrium of the system methane, carbon dioxide, N-methyldiethanolamine (MDEA), and water was measured at pressures up to 200 bar and at the temperatures 313.15 and 353.15 K. The concentration of carbon dioxide in the vapor phase varied between 0.02 and 0.20 mole fraction, and the concentrations of the aqeuous MDEA solution were 0.30 and 0.50 mass fraction. The phase equilibrium was measured in a variable-volume static cell. The pressure in the cell can reach a maximum of 600 bar, and the temperature of the cell can range from 223.15 to 473.15 K.