Phase equilibria for the [{water + 1-methylnaphthalene + p-xylene}] ternary system at T = (573, 623 and 653) K and (4.2 to 20.7) MPa were measured by a flow method. The phase equilibrium measurements were carried out with change of the feed mole fraction of 1-methylnaphthalene in pure water from 0.25 to 0.75. The two phase region of the vapour-liquid equilibria is expanded by increasing the feed mole fraction of 1-methylnaphthalene in pure water. The vapour-liquid-liquid equilibria were found at T = 573 K unlike the (water + p-xylene) binary system. It is found that the type of phase behaviour for the (water + 1-methylnaphthalene + p-xylene) ternary system measured in this work is similar to that for the (water + 1-methylnaphthalene) binary system rather than that for the (water + p-xylene) binary system. (C) 2013 Elsevier Ltd. All rights reserved.