An investigation of SPLITT fractionation is conducted to improve its overall performance. Particular attention is devoted to factors which degrade separation resolution in the thin SPLITT channels, including the development of instabilities due to unstable stratification of density. The presence of these instabilities is quantified using the Richardson number (Ri) and the flow-rate ratio Vover dot (a)/Vover dot (a’), where Vover dot(a) and Vover dot (a’) are volumetric flow rates at the top outlet substream and the top inlet feed substream, respectively. The stability boundary separating the stable and unstable flow domains is identified in terms of these parameters. Based on these criteria, the region most suitable for operation of SPLITT fractionation corresponds to Vover dot (a)/Vover dot (a’) greater than or equal to 8, and Ri in the range of 0.001 to 0.0055, depending upon the value of Vover dot (a)/Vover dot (a’). Experimental verification is provided by the successful separation of a sample of glass bead particles using a multistage fractionation system.