Solid-state C-13 nuclear magnetic resonance (NMR) spectra of humic substances extracted from bauxite and Payer Process liquor have been recorded. Relative to the bauxite humics, the Bayer liquor humics contain less aliphatic and carboxyl carbon and more aromatic carbon. There are corresponding differences in elemental H:C and O:C ratios. However, the liquor fulvic acid proved to have a greater titratable acidity than bauxite fulvic acid, probably as a result of a combination of oxidation processes on the humic macromolecules. The behavior of simple carboxylic acids under Bayer Process-like conditions indicated similar stabilities, with aliphatic compounds being destroyed and aromatic compounds being more stable. The cyclical nature of the process allows the aromatic-rich humics to achieve gram per liter concentrations in the liquor.