To satisfy the global demand, more and more high-quality fuels, pure or converted from heavy oil cuts, like vacuum gas oil (VGO), into highly refined fuels are needed. To meet this increasingly demand, molecular information is mandatory to allow for a detailed characterization of these heavy oil fractions. Several separation techniques have been developed in the last years, among them gas chromatography (GC) and GC x GC are the most widely used ones for obtaining this information. To perform an exhaustive gas chromatographic analysis, all steps must be optimized. In particular, the injection process, which is a key part of the chromatographic process, should ensure the transfer of a representative part of the sample into the columns. This paper will show how the optimization of all programmable-temperature vaporizing (PTV) injection parameters allowed the determination of optimal high-temperature GC x GC (HT-GC x GC) conditions for the analysis of vacuum gas oil avoiding sample discrimination and sample degradation. n-Paraffins recovery from nC(8) to nC(44) was satisfactory and was calculated to be between 93.0 and 100.5% using PTV in splitless injection mode, and between 86.8 and 100.1% in solvent vent mode. A first application of HT-GC x GC using a flow modulator for the analysis of one of the heaviest petroleum cuts is also described. Comparison with other injection techniques showed the possibility to implement PTV, compared to on-column injector, in high-temperature applications for allowing satisfactory recovery of whole sample.