One of the largest problems facing the oil industry today is to characterize fluid and architectural complexities of oil reservoirs. This applies particularly in the development of offshore fields where reservoir reconnaissance is impeded by the high costs of wells, often exceeding $ 100 million. As such, new methods are being developed to address these complexities. Downhole fluid analysis (DFA) is a new method of in-situ fluid characterization used to understand the heterogeneous distributions of hydrocarbon fluids in the reservoir and to identify which crude oils merit subsequent analysis in the laboratory. Comprehensive two-dimensional gas chromatography (GCxGC) is a powerful new method to analyze complex hydrocarbon mixtures such as crude oils and, especially when combined with mass spectroscopy, to elucidate explicit chemical structures. Here, we explore the protocol of DFA coupled with GCxGC to address reservoir complexities.