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The improvement of supercritical fluid chromatography (SFC) instrumentation enhanced its reliability and utility over the past decade. The further development of high speed and high resolution separations is however obstructed by the lack of accurate models for axial dispersion in SFC. In a first step to enhance prediction and understanding of separation performance in SFC, methods need to be developed to measure molecular and longitudinal diffusion in SFC and to model their behavior. These parameters are essential to predict the separation efficiency in chromatography as it affects all contribution (A, B and C-term). Using a commercially available SFC instrument with the addition of only a single rotorstator valve, a flexible method to measure Dmol was developed and validated. By using a chromatographic column to separate the solutes from the injection solvent plug, and a small volume loop to capture and reinject the solute in the appropriate mobile phase, typical practical limitation of this technique could be overcome. The effective diffusion coefficient (Deff) was measured using stop-flow experiments, also called peak parking, where the mobile phase flow is halted when the solute is halfway through the column. In SFC, the set-up needs to be modified since during the parking the mobile phase would decompress and elute from the column. In addition, due to the stronger compressibility of the mobile phase, restarting the flow rate is accompanied by transient start-up effects that vary flowrate and retention in a non-reproducible way. Therefore a two-column variant of the set-up was developed where two identical columns are coupled in parallel using rotor-stator valves, to maintain pressure in the parking column and flow and stable operating pressure in the SFC system.