We have used cyanide-modified Pt(111) electrodes, in combination with cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIRS), and differential electrochemical mass spectrometry (DEMS), to investigate the oxidation of formic acid and methanol on Pt electrodes. Since CO is the poison intermediate formed during the oxidation of both formic acid and methanol, we have previously characterized the CO adlayer on cyanide-modified Pt(111) electrodes. Poison formation on cyanide-modified Pt(111) is nearly completely inhibited in the case of formic acid and methanol, the corresponding electro-oxidation reaction proceeding, hence, exclusively through the reactive intermediate pathway. These results suggest that, in the oxidation of formic acid and methanol, the formation of adsorbed CO would require the presence of at least three contiguous Pt atoms.