Phase equilibrium for two binary systems, (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) mixture, were measured at five experimental temperatures of (313.2, 333.2, 353.2, 373.2 and 393.2) K and pressure from (4.45 to 28.72) MPa. The (vapour + liquid) equilibria for the 1-butyl-2-pyrrolidone and 1-octyl-2-pyrrolidone play a significant role as organic solvents in numerous industrial processes. Both (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) binary mixture systems have critical mixture curves that represent maximums in pressure-temperature diagram between the critical temperatures of CO2 and 1-butyl-2-pyrrolidone or CO2 and 1-octyl-2-pyrrolidone. The (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) systems display type-I phase behaviour. The experimental results for the (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) binary systems are correlated with Peng-Robinson equation of state including two (k(ij), eta(ij)) adjustable parameters. (C) 2018 Elsevier Ltd.