The present study focused on the thermal hydraulic performance improvement of a CO2 gas cooler with the principal goal of reducing its volume, and consequently the necessary charge of the working fluid. To achieve this compactness, the leading methods for supercritical CO2 cooling (including oil effects) were taken from the literature and programmed into a very detailed simulation code, together with the leading air-side flow and heat transfer methods. The effects of tube size, volumetric flow of air, type of air-side fin, miscible oil concentration, etc. were addressed. Compared to an existing design, the volume and refrigerant charge of the CO2 gas cooler were reduced by at least 14%. The simulations with oil showed that there was up to 6% adverse influence on the size of the gas cooler and its CO2 side pressure drop increased up to 2.65 times when oil concentrations of up to 3% were considered. (C) 2016 Elsevier Ltd and IIR. All rights reserved.