Bubble point pressures for pentane + carbon dioxide, octane + carbon dioxide, and pentane + octane + carbon dioxide have been measured in the range 339-450 K. The apparatus has been designed to cover a wide range of temperatures and pressures with a single hydrocarbon load. Carbon dioxide and hydrocarbon compositions are determined gravimetrically by charging known masses into the equilibrium cell. Bubble points are reported for a total of 17 mixtures. To check the experimental technique, the vapor pressure of pentane was measured. Results agreed with the results reported by the Thermodynamics Research Center (Data bases for Chemistry and Engineering TRC Thermodynamic Tables, Version 1.3M; Thermodynamics Research Center : College Station, TX, Dec 1994) within 5%. This may not be considered good enough, but the sample purity was only 99+%. It is well-known that volatile impurities strongly affect bubble point pressures. Simple calculations with the Soave-Redlich-Kwong equation of state (SRK EOS) indicate that a 0.1% nitrogen impurity in pentane at 350 K would raise its vapor pressure (if evaluated as a bubble point) by 17%, while just 0.01% helium would raise this pressure by 6%. The experimental accuracies have been estimated to be approximately 1% in pressure and +/-0.5 degrees C in temperature. These are considered sufficient for most engineering applications, particularly when working with crude oil mixtures.