Conversion of olefins by solid phosphoric acid (SPA) catalysis is a key refining technology for the upgrading of high-temperature Fischer-Tropsch (HTFT) products. Oxygenates present in HTFT material suppress olefin conversion over SPA. A class specific study of SPA catalyzed conversion of alcohols, aldehydes, carboxylic acids, esters, ketones, acetals, and ethers is reported. In addition to well-known acid catalyzed organic reactions, high temperature acid-catalyzed reactions were also observed, such as the conversion of ketones to carboxylic acids and olefins. The following were specifically noted: (a) All of the oxygenates suppressed 1-hexene conversion, and the effect appeared to be related to water production; (b) aldehyde conversion to aromatics, including ethanal to benzene, was observed; (c) tributyl phosphoric acid ester was formed from 1-butanol, but 2-propanol was not converted into tri-isopropyl phosphoric acid ester.