In supercritical fluid chromatography (SCF) the mobile phase is a supercritical gas or a near critical liquid. Compared to gas chromatography, where gas is under ambient pressure, and liquid chromatography, where liquid is used as mobile phase, the solvent power of the fluid mobile phase in SFC can be varied by density, e.g., by pressure changes at constant temperature. Solubility generally increases with pressure under supercritical conditions of the mobile phase. Since temperature is near the critical temperature of the mobile phase, temperature sensitive compounds can be processed. Chromatographic separation can be carried out at constant pressure (isobaric operation) or with increasing pressure (pressure programmed). In addition, temperature can be varied. Temperature directly determines the vapour pressure of the feed components and the density of the mobile phase and, indirectly, adsorption equilibrium. With higher temperature, vapour pressures of the feed components increase exponentially. Density decreases proportionally to temperature if conditions are far from critical, but in the region of the critical point of the mobile phase, which is the main area of application of supercritical fluid chromatography, density varies dramatically with temperature. In this region, the solvent power of the mobile phase, which increases with density, is substantially changed.