In the title compound, C(12)H(15)O(7)PS, the P atom has a distorted tetra-hedral environment. The P-O-C-C torsion angles deviate significantly from zero [average = 12.0 (3)°], indicating that the bicyclic OP(OCH(2))(3)C cage is strained. In the crystal, weak C-H⋯O inter-actions consolidate the packing.