A droplet-in-bubble approach has been incorporated into a previously developed high-pressure droplet vaporization model to study the clustering effects on a liquid oxygen (LOX) droplet evaporating in hydrogen environments under both sub- and supercritical conditions. A broad range of ambient pressures and temperatures are considered. Results indicate that pressure exerts strong influence on droplet vaporization behaviors in a dense cluster environment. Increasing ambient pressure reduces droplet interactions and significantly decreases the droplet vaporization time. The effect of ambient temperature on droplet interactions is found to be very weak. The present study is intended to illuminate the underlying physics of droplet clustering phenomena in combustion devices. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.