In this paper, an experimental study on the near detonation limits for propane-hydrogen-oxygen is performed. Three mixtures (i.e., 8H(2)-C3H8-9O(2), 4H(2)-C3H8-7O(2) and 12H(2)-C3H8-11O(2)) are tested in a rectangular tube (52 mm x 32 mm). Photodiodes with regular intervals are mounted on the tube wall to measure the time of arrival of detonation waves, from which the detonation velocity is determined. Smoked foils are inserted into the tube to obtain the detonation cell pattern. The results indicate that well within the detonation limits, the detonation can propagate at a steady velocity. By reducing the initial pressure, the detonation velocity decreases gradually. Subsequently, the detonation fails as the initial pressure is below a critical pressure. The critical pressures for 8H(2)-C3H8-9O(2), 4H(2)-C3H8-7O(2) and 12H(2)-C3H8-11O(2) mixtures are 4 kPa, 5 kPa and 6 kPa, and the corresponding detonation velocity deficits are 10%, 9%, 10%, respectively. The cellular detonation structures show that the cell size decreases with the decrease of the hydrogen concentration, and the cell structures are very irregular near the detonation limits. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.