So now we have two moles of methane reacting with oxygen. That means, since not one, but two moles of methane are reacting, that means not two, but four moles of oxygen will react to produce our products. That's because two times two is four. That means we're going to produce two moles of carbon dioxide and four moles of oxygen. Now, it's exactly what I said here. Once our reaction runs to completion, two moles of methane and four moles of oxygen are used up to produce two moles of carbon dioxide and four moles of H 20.