We have used a two and one-half dimensiopnal electromagnetic particle code to investigate the collisionless tearing mode under conditions characteristic of the dayside magnetopause. The initial configuration is a tangential discontinuity separating a magnetosheath plasma with a beta of 3 and a vacuum on the magnetosphere side. The plasma consist of electrostatcially coupled ions and electrons. The initial magnetic field consists of a shearing component which reverses sign through the current sheet, and a constant By. The simulation was run for three initial values of &thgr;rot the angle between the magnetic field vectors on either side of the discontinuity of 180¿, 135¿, and 90¿. We have found that the growth rate is a sensitive function of &thgr;rot, with the fastest growth at 180¿. The rate at which magnetic flux is trapped and the total trapped flux also decreases as &thgr;rot becomes significantly less than 180¿. The simulation results are consistent with earlier studies which indicate that the magnetosphere is most unstable to the tearing mode and the largest flux linkage occurs for southward interplanetary magnetic field. ¿ American Geophysical Union 1989