In the work presented in this paper, the propagation direction of the pressure waves generated during combustion-induced Rapid Phase Transition (cRPT) was investigated. To this end, explosion tests were performed for CH4/O-2/N-2/CO2 mixtures in a tubular reactor. Ignition was provided at the top or at the bottom of the vessel. Pressure time histories were recorded by two transducers positioned one at the top and the other one at the bottom. Results have shown that the preferential direction for the pressure waves is that of the flame propagation. When the cRPT phenomenon is weak, an over-adiabatic pressure peak (of around 10-20 bar) can be measured by only one transducer and, in particular, by the transducer far away from the ignition point. Conversely, when the cRPT phenomenon becomes severe, over-adiabatic peaks (as high as 250 bar) can be detected even by the other transducer. Such peaks are the result of separate cRPT events that occur very close to the transducers and, thus, are not damped along the vessel length. In spite of the fact that the upward flame propagation is faster, the cRPT phenomenon is more severe in the case of downward flame propagation. (C) 2016 Elsevier Ltd. All rights reserved.