Numerous aromatic biomarkers such as aromatic carotenoids and aryl isoprenoids have been reported in Brazilian Cretaceous oils. The n-alkyl aromatics such as n-alkyl benzenes (phi-C-n), toluenes (phi(T)-C-n), xylenes, and mesitylenes have also been detected in geological samples and can be valuable tools in geochemical and environmental investigations. In this work, comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCXGC-TOFMS) and GC-tandem MS (GC-MS/MS) were applied to identify the alkyl aromatic series in two crude oils from the Sergipe-Alagoas Basin, Brazil. Geochemical characteristics indicate a different depositional paleoenvironment for each sample, marine and lacustrine end-members. Aromatic compounds were identified using full mass spectrum information, diagnostic ions (i.e., m/z 92 for alkylbenzenes and m/z 106 for alkyltoluenes), selected reaction monitoring transitions, and coinjection with an authentic C-21 n-pentadecylbenzene standard. The Sergipe-Alagoas oils presented a series of n-alkylbenzenes and n-alkyltoluenes ranging from phi-C-7 to phi-C-33 and phi(T)-C-7 to phi(T)-C-30, respectively. In addition, phytanyl arenes and a new series of alpha,omega-bisphenylalkanes were identified for the first time in Sergipe-Alagoas oils. The n-alkylbenzene profile for marine crude oil resembles that of n-alkanes and n-alkylcyclohexanes, which suggests that they may have the same precursors. The investigation of aromatic fractions and detection of n-alkyl aromatic hydrocarbons in Brazilian Cretaceous oils provide new assignments to the contribution of organic matter and its geochemical significance.