Using supercritical CO2as the mobile phase with a 30m × 100μ ID SPB-5 capillary column and temperature of 90°C, high boiling fractions of heavy oils could be characterized. A linear restrictor placed as close as possible to the flame ionization detector jet prevented the characteristic spiking often observed in these systems, and also allowed the study of high molecular weight material without plugging of the restrictor. The boiling points of model saturate and aromatic compounds correlate with retention time providing the capability to study heavy oils without exposing them to the high temperatures necessary in gas chromatography. Individual peaks can be resolved for the n-paraffins in waxes up to C90. Primary production, fireflood and steamflood heavy oils and bitumens were compared by this technique.