The (T, p, x) surface of (liquid + liquid) phase equilibrium has been investigated in the vicinity of the line of lower critical solution points of [(1 - x)H2O + x(CH3){CH3(CH2)4}2PO]. Measurements were carried out in a high-pressure optical chamber at pressures p in the range from 0.1 MPa to 230 MPa. The behaviour of critical exponents for (p, x) and (T, x) phase-equilibrium diagrams : beta(T) and beta(p), respectively, has been studied along the critical line and at the double critical point (DCP) with coordinates p(D) = 127 MPa and T(D) = 296.5 K. The exponent beta(p) retains its value along the line of critical points, including the double critical point; beta(T) increases anomalously with an approach to the DCP.