Accuracy is the most important issue when performing compound-specific stable isotope analysis of polycyclic aromatic hydrocarbons (PAHs) extracted from complex samples. It depends on two main factors: the possible isotopic fractionation of the compounds during extraction and the potential co-elution with interfering compounds with different isotopic signatures. Herein, a simplified pressurised liquid extraction method for compound-specific stable isotope analysis of PAHs in non-aqueous-phase liquids of coal tar is presented. Samples extracted using the new method and by fractionation on a silica gel column were analysed by comprehensive two-dimensional gas chromatography. It was possible to evaluate the effect of co-elution on the carbon and hydrogen stable isotope signatures of the 16 US EPA priority PAHs in coal tars with various proportions of aromatic and aliphatic content. Even in samples that presented a good baseline resolution, the PAHs of interest co-eluted with other aromatic compounds with a notable effect on their stable isotope values; this demonstrated the necessity to check the quality of all extraction and clean-up methods (either the simplified pressurised liquid extraction or more traditional labour-intensive methods) for more complex samples prior to data interpretation. Additionally, comprehensive two-dimensional gas chromatography enabled visualisation of the suspected co-elution for the first time.