Methanol/CO2 phase behavior was investigated previously by a number of researchers. However, the entire composition range at moderate temperatures was not mapped in a single study. Extensive acetonitrile/CO2 vapor-liquid phase information has not been reported. The goals of this research were twofold : (1) to demonstrate the accuracy and precision of visual observation for vapor-liquid phase boundary determination using a high-pressure, variable-volume view cell with the methanol/CO2 system relative to the data available, and (2) to examine phase behavior of methanol/CO2 and acetonitrile/CO2, commonly used binary fluids for supercritical fluid chromatography and extraction, from 0-1.00 mole fraction CO2 and over a 25-100 degrees C temperature range. Results for methanol/CO2 were found to be very comparable to the literature values.