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High-fidelity numerical simulations using a Graphics Processing Unit (GPU)-based solver are performed to investigate oblique detonations induced by a two-dimensional, semi-infinite wedge using an idealized model with the reactive Euler equations coupled with one-step Arrhenius or two-step induction-reaction kinetics. The novelty of this work lies in the analysis of chemical reaction sensitivity (characterized by the activation energy <i>E</i>_a and heat release rate constant <i>k</i>_R) on the two types of oblique detonation formation, namely, the abrupt onset with a multi-wave point and a smooth transition with a curved shock. Scenarios with various inflow Mach number regimes <i>M</i>₀ and wedge angles <i>&#952;</i> are considered. The conditions for these two formation types are described quantitatively by the obtained boundary curves in <i>M</i>₀&#8722;<i>E</i>_a and <i>M</i>₀&#8722;<i>k</i>_R spaces. At a low <i>M</i>₀, the critical <i>E</i>_a,cr and <i>k</i>_R,cr for the transition are essentially independent of the wedge angle. At a high flow Mach number regime with <i>M</i>₀ above approximately 9.0, the boundary curves for the three wedge angles deviate substantially from each other. The overdrive effect induced by the wedge becomes the dominant factor on the transition type. In the limit of large <i>E</i>_a, the flow in the vicinity of the initiation region exhibits more complex features. The effects of the features on the unstable oblique detonation surface are discussed.