The Solubility of carbon dioxide in aqueous Mixtures of 2,2'-methyliminodiethanol (N-methyldiethanolamine, MDEA) and 1,4-diazacyclohexane (piperazine, PZ) was measured at low gas loadings (at stoichiometric molar ratios of carbon dioxide to (MDEA + PZ) between about 0.02 and 0.83) and consequently low partial pressures of carbon dioxide (from about (0.1 to 150 kPa) at three temperatures (313 K, 353 K, and 393 K) by headspace gas chromatography. The molality of MDEA in the aqueous mixture was varied between (2 and 8) mol.(kg of water)(-1) and the molality of piperazine was varied between (1 and 4) mol.(kg of water)(-1). The new experimental data supplement recently published high-pressure data for the same systems. Comparisons with prediction results from a formerly published thermodynamic model reveal that the set of model parameters from that previous publication should be revised.