It is interesting to note that the results of the present study point to less compressor stages being more optimal when a significant pressure drop between compression stages is accounted for. For the Gorgon injection and storage project inline compressor with fewer inter-cooling stages were selected over an integrally geared compressor with 8 compressor stages due to significant pressure drop in inter-coolers and long inter connecting piping (air coolers located away from compressor package) among other things. In that respect the results obtained with the present model seem to support this selection. Following the compression only case for pressurisation of CO 2 , the concept of compression followed by pumping is introduced and investigated. Below the critical pressure, cooling/liquefaction is required and managed by a refrigerant cycle using ammonia, although use of other refrigerants is possible too. Above the critical pressure, liquefaction as such is not occurring, instead, the CO 2 is pumped at the conditions directly after the discharge cooler of the final compression stage . An initial case (case 1) is investigated, which considers the same inputs as the one investigated in the previous section for compression only, in terms of inlet flow, starting and final pressure, and compressor discharge cooler temperature. The main difference is that instead of explicitly defining the number of compression stages, a maximum pressure ratio per stage/section of 2 is applied, which mimics an integrally geared compressor. Further, a fixed pressure drop between compression stages of 0.3 bar is applied. Compression occurs from the initial pressure of 1.5 bar up to the pressure where pumping is initiated (a pressure between 15 and the final pressure of 150 bar). This pressure is referred to as the liquefaction/pumping pressure. The results are shown in Figure . In the special case where the pumping pressure equals the final pressure, the case is effectively a compression only case.