Majority of HPLC applications are covered under reversed phase chromatography. Stationary phases mostly comprise of non polar alkyl hydrocarbons such as C-8 or C-18 chains bound to Silica or other inert supports. C18 columns actually can handle more than 60% of the applications in most HPLC labs. Mobile phase is polar and the elusion order is polar followed by less polar and weakly polar or non-polar compounds in the end.