The traditionally used refrigerant in mobile air conditioning (MAC), R134a, has a high GWP of 1,300 and is to be banned in EU market for new passenger cars and light commercial vehicles from January 1, 2017. In US, EPA has listed R134a as unacceptable for new light-duty vehicles beginning in Model Year 2021. The natural refrigerant, R744 (CO2), remains a viable solution to replace R134a due to its environmental friendliness, low cost, non-flammability, and high volumetric heat capacity. One challenge of R744 vapor compression system is reduced efficiency with ambient temperature. Prior research has demonstrated that a parallel or multistage compression cycle represents a superior design to a conventional single-compression cycle in that it not only improves the optimum cooling efficiency, but also brings down the optimum discharge pressure. In this study, thermodynamic analysis is performed on a transcritical CO2 cycle with parallel or multistage compression under typical MAC conditions. Characteristics on improvement of cooling COP and reduction of discharge pressure with respect to evaporating temperature and gas cooler exit temperature are described. A correlation of optimum discharge pressure as a function of these two parameters is developed for potential use in dynamic control algorithms. Finally, this study discusses various prototype compressor designs and system configurations for implementation of parallel or multistage compression technology.