We present a study of the Bose-Einstein interference effect for pions of equal charge and similar momentum vectors in inclusive antiprotonproton reactions at 9.1 GeV/c. The results are used to provide an estimate of the space-time dimensions of the region emitting the pions. We obtain an average radius R = 1.3 rt 0.1 fm and a time of emission CT = 0.9 * 0.2fm. The parameter h, a measure of the fraction of interfering likecharge pions, js found to be h = 0.8 c 0.1. No large deviation from a spherical shape of the pion source is observed. We emphasize the importance of establishing a non-interfering background.