This study examines the optimal operation of the dual mixed refrigerant (DMR) process by steady-state optimality analysis. The purpose of this analysis is to discover the optimizing variable that can maintain the DMR process in the optimal compressor duty. First, a rigorous dynamic simulation of the DMR process was built in the Aspen Hysys interface. Second, numerous step tests on the refrigerant flow rate were conducted and the resulting total compressor duty was recorded. The steady-state operational map that correlates the refrigerant flow rate and total compressor duty was drawn to locate the optimal operation region of the DMR process. The map also contains information on the state variables in the DMR process that in particular combinations, will allow the process to be operated at the optimal compressor duty. The comprehensive information on the map makes it an excellent tool for selecting the proper optimizing variable for the DMR process. The resulting steady-state optimality map suggests that, when the flow rate ratio of the two refrigerants (WMR/CMR ratio) is kept constant, the operational of DMR process will remain within optimal region. This suggests that the WMR/CMR ratio is the proper optimizing variable for the DMR process. From a control viewpoint, the control structure that includes the WMR/CMR ratio loop also showed excellent performance compared to the other possible structures in terms of maintaining the stability and fulfulling the control objectives of the DMR process.