This paper is aimed at providing some data on the detonability of methane mixtures at a high initial pressure. The relevant work that has been performed so far was based on a conventional source of ignition, i.e., a blasting cap. Following these initiation experiments at the French German Research Institute (ISL), two sets of experiments were performed in CH4/Air mixtures, at initial pressures in the range of 0.1 to 3.7 MPa, at the University of Washington (UW): (1) using a piston that directly enters the test section in the velocity range of 1100–1800 ms−1 and (2) the piston impacts an intermediate section of CH4/O2. An additional series of experiments was performed using an initiator stage of stoichiometric CH4/O2 ignited by a 150 J conventional fuse cap.