Elemental analysis, Fourier transform infrared, C-13 nuclear magnetic resonance, and electrospray ionization/mass spectrometry (ESI/MS) experiments were performed on two commercial naphthenic acid mixtures in order to determine the acidity, ring type, and carbon number distribution. Critical MS/TMS experimental parameters, i.e., isolation width and collision-activated dissociation energy, were optimized and fragmentation patterns elucidated for a series of acid standards and the commercial naphthenic acid mixtures. The MS/MS experiments confirm that P&B and Fluka naphthenic acid mixtures consist primarily of carboxylic acids with dominant hydrogen deficiency values of -6 and 0, respectively, with respect to an alkanoic acid reference. The MS/MS experiments validated the preponderance of carboxylic acid moieties in these samples. The approach was then used to determine the composition of a Maya crude oil extract. Surprisingly, the extract was found to contain a dominant alkylsulfonic acid homologous series.