In this work, the absorption process of carbon dioxide is performed in a custom designed high pressure experimental setup in which the gas and nanofluid are in direct contact at static state in a closed vessel. The initial condition of the tests are set at 20, 30, and 40 bar and 308 K. Nanoparticles of SiO2, Al2O3, Fe3O4, and carbon nanotubes (CNTs) are dispersed in pure water to form nanofluids at concentrations of 0.02, 0.05, and 0.1 wt %. Also, CNT nanoparticle has been dispersed in methyldiethanolamine and diethanolamine aqueous solutions at the concentration of 0.02 wt %. The absorption performances of different nanofluids are compared with the base solutions and with other nanofluids at different conditions. The results show that SiO2 and Al2O3 are more effective at higher nanoparticle concentrations (0.1 wt %), and they can enhance the absorption capacity up to 21% and 18%, respectively. Fe3O4 and CNT are more effective at lower nanoparticle concentration (0.02 wt %), and they can increase it up to 24% and 34%, respectively. CNT nanoparticle is more effective for methyldiethanolamine solution compared to diethanolamine solution with an increase in the absorption capacity up to 23%. It seems that gas adsorption on the nanoparticles surface leads to higher absorption capacity of nanofluids at equilibrium condition. [ABSTRACT FROM AUTHOR]