The applicability of the Langmuir EOS is also established for petroleum derived asphaltenes extracted from Kuwaiti UG8, coal-derived, and synthetic asphaltenes (Figure ). Analysis of surface excess coverage for petroleum-derived, coal -derived and synthetic asphaltenes yielded approximately 6 ring core, 4 ring core and a 13-ring core, respectively. The estimates of mean number of rings in aromatic core from interfacial measurements are consistent with the Asphaltene adsorption at oil-water interface is found to be primarily of asphaltene monomers and suggest the lack of interfacial activity of nano-aggregate as: (a) below the CNAC, the slope of interfacial tension decay evolves similarly to asphaltene monomer concentration from nuclear magnetic resonance (NMR). (b) The values of the slopes are consistent with those for adsorption of monomers with higher diffusivities compared to that of nanoaggregates ). These differences in views and observations of the structure of the adsorbed layers still remain to be reconciled.