X-ray escape peaks for a planar HPGe detector were investigated for a point source of photons with 59.5 keV energy. The effect of the solid angle for the incident photons on the escape probability of Ge K x-rays was studied using collimators with varying apertures. A Monte Carlo program was also developed to estimate the probability of escape for various mechanisms and routes. The experimental and simulation results showed that the escape probability is essentially constant for a wide range of collimator radii, but at first starts to increase and then becomes constant when the side surface of the detector becomes accessible for escape with larger collimators. Copyright (C) 2003 John Wiley Sons, Ltd.