The three H atoms of the oxonium H30+ cation are disordered equally over four orientations and are involved in an extensive three-dimensional hydrogen-bonding network with the carbonyl and carboxylate O atoms of four neighbouring (Ph)CH(OAc)COO- anions [H...O 1.62- 1.85, O...O 2.722(3)-2.902(3) A]; the O-acetyl oxygen is not involved in any hydrogen bonding, Principal bond lengths include Cs:--Ocarbonyl 1.211(4), Csp 2- Oearboxylate 1.234(4) and 1.246(3) ,4,. The main torsion angles defining the conformation in the mandelate anion are: Ocarboxylate--Csf--Csp a-Car 84.6(2) and -92.3(2)°; Csp 2-O -- Csp 3- Car -- 171.6(2) and Csp 2 --O --Csp 3 -- Csp 2 67.7(2) °.