The present disclosure relates to solid phosphoric acid (SPA) catalysts useful in the conversion of hydrocarbons, such as the oligomerization of olefins, to methods for making such SPA catalysts, and to methods for converting hydrocarbons by contacting hydrocarbons with such catalyst. For example, in certain embodiments, the disclosure provides a calcined solid phosphoric acid catalyst composition that includes phosphoric acid and silicon phosphates, and in which (i) one or more promoters each selected from the group consisting of boron, bismuth, tungsten, silver and lanthanum is present; (ii) the composition is a calcined product of a formable mixture including silica-alumina clay, silica fiber and/or silica alumina fiber; or (iii) the composition is a calcined product of a formable mixture including fumed silica.