Improved methods for separation and quantitative determination of hydrocarbon types from gas oil have been developed, which were based on high-performance thin-layer chromatography with ultraviolet and fluorescence scanning densitometry using horizontal elution. One of the methods allows the separation, detection, and determination of alkanes and naphthenes to be carried out, using berberine-impregnated silica gel HPTLC plates, elution with n-hexane, and berberine-induced fluorescence detection at 365 nm. Another developed method allows total aromatics to be determined using silica gel HPTLC plates by elution with n-hexane and acetone, and UV detection. In turn, PACs over three aromatic rings can be determined on either silica gel or caffeine-impregnated silica gel HPTLC plates, elution with n-hexane, and selective detection using native fluorescence at 365 nm. Concentrations lower than 5 wt% can be determined using this technique. In addition, a technique for an efficient, baseline-resolved separation of a gas oil according to the number of aromatics rings (mono + di-, tri-, and polyaromatic compounds with more than three rings) is presented here. This technique involves a multistep elution on a mixed (silica gel and caffeine-impregnated silica gel HPTLC plate) using a counter-elution device, and UV detection.