The design of any process involving supercritical fluids requires some degree of knowledge about the thermophysical and chemical properties of the solvents, solutes, and of the solvent + solute mixture. This knowledge can take the form of measured data, models based on measured data, or predictions. Clearly, the most costly approach is to obtain measured data for each property of interest, and the least accurate is to use predictions throughout. The best compromise is therefore the use of physical and engineering models that are based on measured properties that have a known and acceptable uncertainty. In this review, we cover the experimental aspects of the data required for process design with supercritical fluids. For clarity, the measurement techniques are divided between properties of pure components ( solvents and solutes) and properties of mixtures. For pure components, we begin with the solvents, and discuss the fundamental P-V-T surface of a fluid, and then consider viscosity and thermal conductivity, solvent interaction properties, and finally, chemical stability. For the pure solutes, we discuss the solute vapor pressure and chemical stability. Then, the properties of supercritical fluid mixtures (solvent + solute) are discussed. Here, considerable time is devoted to the measurement of solute solubility. We also discuss aspects of solute diffusion and vapor/liquid equilibrium.