Solubilities and liquid-liquid-phase equilibria for the ternary system water + phosphoric acid + tributyl phosphate are presented at (298.15 and 323.15) K. The binodal curves, tie lines, and distribution curves have been determined. The plait point compositions have been calculated by Hand's method. The extraction power of tributyl phosphate for phosphoric acid has been compared to those of methyl isobutyl ketone, dibutyl ether, isoamyl alcohol, and diethyl ketone. The extraction chemistry of H3PO4 by tributyl phosphate is also discussed.