The structural and molecular characteristics of the asphaltenes of four oils-light oil, L-O; medium oils, M1-O and M2-O; and heavy oil, H-O-from the Weyburn and adjacent areas in Saskatchewan, Canada were determined and correlated with the oils' asphaltene precipitation behavior and mechanism, as well as their chemical inhibitor effectiveness, for the purpose of determining differences between CO2 and hydrocarbon flooding for enhanced oil recovery (EOR). A multitechnique approach involving Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (H-1 NMR) spectroscopy, C-13 NMR spectroscopy, gated spin-echo (GASPE) spectroscopy, inductively coupled plasma (lCP), elemental analysis, saturates-aromatics-resins-asphaltenes (SARA) analysis, molecular weight, and density studies was used for characterization of the crude oils and their n-heptane-derived asphaltenes. Results showed that the asphaltene precipitation behavior and mechanism each were strong functions of the oil and asphaltene characteristics. Interestingly, there were striking contrasts in these relationships, depending on whether CO2 or n-heptane was used as the flooding (i.e., precipitating) agent. In addition, there were differences in the inhibition effectiveness and mechanism, depending on the type of flooding agent used. Furthermore, these differences also were dependent on the type of chemical inhibitor used.