Classical molecular dynamics simulations were used to study the separation of carbon dioxide from methane by three formulations of the deep eutectic solvent (DES) ethaline (choline chloride: ethylene glycol at 1:2, 1:4 and 1:8 molar ratios), in the bulk and confined inside carbon and titania slit pores of two different pore widths, 2 nm and 5 nm. The highest permselectivities (~20) are observed for 1:2 ethaline in a 5 nm carbon pore, followed by the 1:4 DES in a 5 nm graphite pore, 1:2 ethaline in a 2 nm carbon pore and the 1:8 bulk DES. Our results indicate that variations in the ratio of ethylene glycol, which in turn affect the interactions of all DES species with the gas molecules and the different pore walls, plus confinement effects resulting from varying the pore sizes, can affect the gas separation performance of these systems in complex ways.