Solubility and tie line data-have been measured for bis(2-methylpropyl) ether + phosphoric acid + water at 25, 51, and 60 degrees C. This system presents a-three-phase region at temperatures greater than 49.5 degrees C. The extension of the two-phase region, as well as that of the three-phase region, increases with temperature (i.e., decreasing solubility). The behavior of this system has been compared to those of dipropyl ethers (bis(1-methylethyl) ether, dipropyl ether, and 1-methylethyl propyl ether), showing the influence of chain branching on the appearance of the three-phase region.