State-resolved measurements of CH4 reactivity on Ni(111) and Ni(100) have yielded detailed insights into how methane’s vibrational energy promotes reactivity. To date, such measurements have relied on post-dose quantification of reaction products to measure reactivity as a function of methane’s translational energy, internal vibrational and rotational state, and surface temperature. Here, we describe a new detection scheme for measuring state-resolved reaction probabilities. This method uses a variation of the “King and Wells” molecular beam reflectivity method to improve reproducibility and significantly decrease the data acquisition time for state-resolved measurements. Rather than modulate the flux of molecules incident on the surface, we modulate laser excitation. In this way, the partial pressure change due to modulation reveals the difference in reactivity with and without laser excitation, which is the key quantity needed to obtain state resolved reaction probabilities. We demonstrate the method for methane incident on Ni(111) and show that it provides real-time coverage dependent reaction probabilities while decreasing data acquisition time and permitting a more expansive exploration of how energy and chemical identity influences reactivity at the gas-surface interface. We use this experimental method to extend our study of CH4 activation to additional vibrational states, including the 2ν4 bend overtone, and different surfaces. Comparing the reactivity of these states provides insight into key features of energy flow during the reaction, and data to assess the generality of non-statitical behavior in gas-surface reactivity.