Some 40 % of the world’s remaining gas reserves are sour or acid, containing large quantities of CO2 and H2S and other sulfur compounds. Many large oil and gas fields have more than 10 mole % CO2 and H2S content. In the gas processing industry absorption with chemical solvents has been used commercially for the removal of acid gas impurities from natural gas. Alkanolamines, simple combinations of alcohols and ammonia, are the most commonly used category of chemical solvents for acid gas capture. This Ph.D. project is aboutthermodynamics of natural gas cleaning process with alkanolamines as solvent, modeling and experimental study. The project is collaboration between DTU and Statoil. Thermodynamic modeling is being done at DTU and experiments were performed at Statoil laboratories. In modeling part of the project, thermodynamic models were developed for CO2-MDEA-H2O, CO2-MEA-H2O, CO2-MDEA-MEA-H2O, H2S-MDEA-H2O, H2SCH4-MDEA-H2O systems and the constituent binary subsystems of the mentioned mixtures. The experimental part of the project includes vapor-liquid equilibrium measurements for CO2-MDEAH2O and CO2-MDEA-PZ-H2O at atmospheric pressure, high pressure vapor-liquid equilibrium experiments for H2S-CH4-MDEA-H2O, density measurements for aqueous MDEA and aqueous activated MDEA and piperazine solubility measurements in aqueous MDEA. Different commercial simulators together with the developed Extended UNIQUAC model were used to simulate the experimental data points. The effect of total pressure on acid gas solubility was also quantitatively investigated through both experimental and modeling approaches.