We report, a new method for the detailed speciation and quantification of low levels of conjugated dienes (diolefins) in complex hydrocarbon matrixes, such as steam-cracked naphthas, catalytically cracked naphthas, and heavy coker naphthas. Conjugated dienes are responsible for hydrocarbon polymerization (fouling) in various refinery processes. Until now, complete analysis of conjugated dienes, particularly C-6+ conjugated dienes, was almost impossible, because of their low concentrations and severe matrix interference. Here, we show that selective derivatization of conjugated dienes with MTAD, in combination with gas chromatography-chemical ionization mass spectrometry (GC/CIMS) and gas chromatography-nitrogen chemiluminescence detection (GC/NCD) can be used to analyze the total conjugated dienes (up to C-10) in various hydrocarbon matrixes quantitatively.