The heats of absorption of CO2 in aqueous tertiary amines (N-methyldiethanolamine (MDEA), 3-dimethylamino-1-propanol (3DMAP), and 1-dimethylamino-2-propanol (1DMAP)) were measured using a flow calorimeter at different temperatures (298.15, 313.15, and 343.15 K) and pressures (2 and 5 MPa) for 5 and 30 wt %. The integral heat of absorption and the indirect solubility limit were determined using the experimental data. The heat of absorption values were correlated using a rigorous thermodynamic model. The temperature dependent heats of reactions and the equilibrium constants for amine protonation reactions were calculated using the model. Comparisons were made with the integral heat of absorption values obtained from phase equilibrium measurements for MDEA using the Gibbs–Helmholtz equation. 3DMAP was found to have a higher CO2 loading capacity (molCO2/molamine) and a higher reaction rate with a similar heat of absorption when compared to other popular tertiary amines (MDEA and triethanolamine (TEA)).