The electron drift mobility (mu) was measured by a time-of-flight method in pure liquid o- and m-xylene under high pressures up to 300 MPa, and in the temperature ranges from 15 to 120 degrees C and 0 to 100 degrees C, respectively. In both liquids mu increases in the lower pressure region at lower temperatures. At higher pressures mu decreases gradually with pressure at all temperatures studied. The pressure dependence of mu was interpreted in terms of a two-state model and a hopping model. When mu increases with pressure this interpretation leads to a positive volume change upon introduction of electrons into the liquid, showing electrons reside in cavities of radius 0.31 to 0.32 nm, whereas in the high pressure region electron attachment to xylene molecules occurs, accompanied by hopping of electrons between molecules.