The hydrogen-bonding basicity of asphalts, oxidized asphalts, and asphalt fractions has been investigated by infrared techniques using phenol as the hydrogen-bonding acid. Evidence has been obtained that asphalts exhibit strong hydrogen-bonding basicity. Infrared frequency shift data give enthalpies of formation in the range 6 to 8 kcal/mole for the asphalt-phenol hydrogen bond in ccl4 solution. The phenol interaction data suggest a hydrogen-bonding base concentration of at least 2 moles per gram of asphalt. Air oxidation of asphalts at elevated temperatures increased the measured hydrogen-bonding basicity of the asphalt and suggests the formation of new hydrogen-bonding bases. Sulfur-containing molecules are suggested as important to the hydrogen-bonding basicity of asphalts, and the oxidation of the sulfur in these molecules could account for some of the increased basicity on air oxidation. Data from the methylation of an asphalt and its fractions with diazomethane suggest the occurrence of molecular aggregation via hydrogen bonding.