We present continuous flow field desorption ionization Fourier transform ion cyclotron resonance mass spectrometry (FD FT-ICR MS) as a method for detailed speciation of aromatic compounds in fractionated crude oils and petroleum refinery process streams. The high efficiency for field desorption ionization of nonpolar molecules combined with the unparalleled mass resolving power and mass accuracy of FT-ICR MS enable unequivocal elemental composition assignment for similar to 700-1400 species for each of four samples in the present analysis. On the basis of the elemental composition assignments, we present complete class and type determination for enriched aromatic fractions from refinery process streams, including high-sulfur vacuum gas oil, low-sulfur vacuum gas oil, fluid catalytic cracking bottoms, and a coker vacuum gas oil. These process streams were selected to demonstrate FD FT-ICR MS capability for a variety of compositional scenarios. The data obtained by FD FT-ICR MS are qualitatively consistent with the predicted characteristics of the refinery process streams. Combined with our prior electrospray ionization results, FT-ICR MS analysis now spans petroleum components ranging from metalloporphyrins, basic nitrogens, nonbasic nitrogens, and acids to aromatics and thiophenoaromatics.