The density of methanol‐carbon dioxide mixtures has been measured at 40, 50, and 60°C and the data presented as constant density curves in plots of pressure against composition. Mixtures containing from 1 to 23.5% methanol were covered. The density information was compared with liquid‐vapor equilibria data from the literature and with results from chromatographic separations using both sub‐ and supercritical conditions. The results indicate that phase transitions do not usually occur when the concentration of the modifier is increased while holding temperature and pressure constant. Similarly, no phase transition occurs when the temperature is increased from 28 to 80°C, at a constant (high) pressure and modifier concentration.

Binary fluids with many desirable compositions cannot be prepared at low densities: densities below 0.4–0.5 g/cm³ cannot be obtained from methanol‐carbon dioxide mixtures because the fluids separate into two phases. This means that density programming with many binary fluid combinations will be of secondary importance compared with composition programming.