In general, if two adsorbates have similar ϵ s values, they are likely to scale. Figure shows ϵ s for a range of re-normalised energy levels ϵ a . Since each ϵ s value corresponds to a specific ϵ a value for each row of transition metals, it suffices to say that two adsorbates with similar ϵ a are likely to scale. This condition is satisfied for scaling relations between adsorbates binding to the metal with the same atom, such as C* vs. CH x * (x = 1, 2, 3), COOH* vs CO* 32 or OOH* vs OH*. It does not hold for adsorbates with very different ϵ s and corresponding ϵ a , such as C* and O*.