Electrocatalysis is the science of modifying the overall rates of electrochemical reactions so that selectivity, yield and efficiency are maximized. Studies in electrocatalysis have resulted in tools such as highly selective multicomponent gas mixture sensors and better electrocatalysts for the fuel cells. Markovic and Lucas have been very active in studying the mechanisms by which these catalysts operate and developing in-situ surface x-ray scattering (SXS) techniques for their studies. SXS capabilities at SSRL were recently used to investigate the interface structure of an ultrathin carbon monoxide overlayer on platinum. Carbon monoxide is the simplest C₁ molecule that can be electrochemically oxidized in a low temperature fuel cell at a reasonable (although not necessarily practical) potential. It thus serves as an important model "fuel" for fundamental studies of C₁ electrocatalysis.