The membrane separation process offers a promising solution for syngas components separation and adjusting the ratio of the components. The multicomponent separation process is however complex and cannot be easily described. The presented study offers a comparison of ideal and real selectivities for three H2-CO-CO2 model mixtures containing 15-35 mol% H2, 35 mol% CO, and 30-50 mol% CO2. The mixtures were tested with total pressure drops 0.5-8 bar (retentate pressure from 2 to 10 bar with the permeate pressure levels of 1.2 bar, 2.5 bar, and 4 bar). The membrane module used in the study is a hollow fiber polyimide membrane module with 3000 hollow fibers with an inner diameter of 0.188 mm and a length of 290 mm with an active separation layer. The ideal selectivities for are a(H2/CO2) = 3.21 and a(CO2/CO) = 14.77. The experimental results show that with increasing stagecut, the selectivities drop to below 1.3 for H2/CO2 (40 % of the ideal selectivity) and to below 1.4 for CO2/CO (9.5 % of the ideal selectivity). Also, the selectivity decreases at a different rate for both different feed compositions and different permeate pressures. The H2/CO2 selectivity drops faster for lower permeate pressure, the CO2/CO selectivity drops faster for higher permeate pressure. The separation factors increase both for H2/CO2 and CO2/CO with increasing pressure differences. Also, with the lower permeate pressure (pP = 1.2 bar) both separation factors (for H2/CO2 and CO2/CO) increase at a greater rate.