The solubility of hydrogen sulfide in an aqueous mixture of 2,2'-methyliminodiethanol (N-methyldiethanolamine, [CAS 105-59-9], MDEA) and 1,4-diazacyclohexane (piperazine, [CAS 110-85-0], PIPH2) was measured over a wide range of gas-loadings (stoichiometric molar ratios of hydrogen sulfide to (MDEA + PIPH2) between about 0.014 and 1.67) at three temperatures (about 313 K, 353 K, and 393 K) by headspace gas chromatography as well as by a synthetic gas solubility method. The molality of MDEA in the aqueous mixture was about 4.5 mol.(kg water)(-1) and that of PIPH2 about 1.6 mol.(kg water)(-1). The headspace gas chromatography technique was applied in the low pressure range (partial pressure of H2S between 0.64 and 125.7 kPa, stoichiometric molar ratio of H2S to (MDEA + PIPH2) between about 0.014 and 0.73). The synthetic method was applied in the high pressure range (total pressure between 0.2 and 5.5 MPa, stoichiometric molar ratio of H2S to (MDEA + PIPH2) between about about 0.51 and 1.67). The new experimental results are compared to prediction results from a thermodynamic model that was parametrized using only experimental results for the solubility of H2S data in the aqueous solution of the single amines in the high pressure range.