By means of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), we identify nonvolatile polar acidic and basic emulsion stabilizers in nine geographically distinct light, medium, and heavy oils. Although oil class distributions are unique, oils of similar API specific gravity exhibit similar relative abundances for the O-2 and O4S classes. Heavy oils are high in O-2 and low in low in O4S. The light oils follow the opposite trend. However, independent of parent oil O-2 and O4S class abundances, O-2 and O4S species preferentially adsorb and are the two most abundant classes in the emulsion interfacial material. Negative-ion nitrogen-containing classes do not have a high affinity for emulsion interface adsorption. However all positive-ion nitrogen-containing species adsorb to the oil/water interface.