A study is made of the initiation of gas dynamical processes during the induction period of a high activation energy supercritical thermal explosion in a reactive gas confined between two infinite parallel plates. Solutions are assumed to vary. spatially only in the direction perpendicular to the plates. The detailed development of the density, velocity, temperature, and fuel mass fraction fields during the induction period is separated into three phases. During the first phase, occurring on the acoustic time scale of the vessel, conduction-dominated boundary layers generate an acoustic field in a nondissipative interior core region. The second phase, occuring on the conduction time scale of the vessel, is characterized by a pointwise competition between reaction-generated heat release, conduction, and compression. The Frank-Kamenetskii criteria dividing super-and subcritical systems is found to be the same as that for rigid explosive materials. In a supercritical system, /i > 5crit, the third phase, of extremely limited duration, is dominated by the development of a tiny self-focusing hot spot embedded within a nearly invariant conduction-dominated field filling most of the vessel. The rapid gas expansion in the hot spot is the source of further, more dramatic gas dynamical processes. The thermal runaway time for the gas system is found to be reduced by about 25% from that for an analogous rigid explosive over a wide range of values of the Frank-Kamenetskii parameter 8.