Electrospray ionization (ESI) coupled with Fourier ion cyclotron resonance mass spectrometry (FTICR MS) has been successfully used for molecular characterization of petroleum. However, ESI can not ionize nonpolar components which generally are dominant in the petroleum fraction. Here, we introduce a novel approach for aromatic compounds molecular characterization. Aromatics in petroleum fractions were ionized to [M + H](+) by positive-ion ESI with HCOONH4 as an ionization promoter, and when ESI is combined with high resolution FTICR MS, aromatic hydrocarbons and heteroatoms in petroleum fractions can be simultaneously analyzed. The method is easily available and has potential for the characterization of aromatic compounds in any other matrix.