A maximum bubble pressure apparatus, described in a previous publication, has been used at pressures to 13.9 MPa (2000 psig) and temperature to 623 K (350degreesC) to measure the static surface tension of several alkanes and paraffinic petroleum fractions, and two types of Alberta bitumens in contact with hydrogen, helium and hydrogen/methane mixtures. With hydrogen, the surface tensions of alkanes or mixtures of alkanes were nearly independent of pressure, whereas with helium surface tension increased significantly. With hydrogen/ methane mixtures, the surface tension decreased in value as pressure increased, with the effect increasing at the higher methane concentrations. For the two bitumens used, the surface tension with hydrogen showed a 10-15% increase as pressure increased at constant temperature. Some discussion is also given concerning methods of predicting the effects of pressure and temperature in hydrogen/hydrocarbon systems.