Standing waves are a special type of spatio-temporal pattern observed in the CO oxidation reaction on Pt(110). We present new experimental data that indicate the important role played by the formation of subsurface oxygen. The formation of these patterns is correlated with reflective collisions of traveling waves that have previously been found in the same reaction. We also show that global coupling through the gas phase and external forcing are essential for stabilizing and synchronizing the standing wave patterns. The principal properties of the observed patterns are reproduced by numerical simulations based on an extended reaction-diffusion model.