We have used polymer density functional theory to study the surface tension behavior of heavy hydrocarbons and their binary mixtures with CO2, for which very limited data is available in the literature. Dodecane (C12H26), tertacosane (C24H50), and hexatriacontane (C36H74), and their CO2 binary mixtures have been studied over a wide range of temperature (313-423 K) and pressure (ambient to 30 MPa) conditions representative of typical petroleum reservoirs. We have compared three parameterization schemes and showed that parameterization using critical constants gives surface tension results that are in very good agreement with the available experimental data. The most significant result from this study is the double crossover behavior in the surface tension of the alkane-CO2 binary mixtures, resulting from the simultaneous changes in liquid density and CO2 solubility. (C) 2011 Elsevier B.V. All rights reserved.