(JP10029803-A)      A production method for a hydrogen-containing gas for fuel cells comprises: (a) adding oxygen-containing gas to a hydrogen-containing gas containing carbon monoxide (CO), prepared by the reforming reaction of an organic compound, to give a mixed gas; and (b) bringing the mixed gas into contact with a catalyst composed mainly of ruthenium metal and having not less than 1 mmol/g-ruthenium CO adsorption and not less than 0.5 CO adsorption index, to oxidise and remove the CO. The CO adsorption index is given by: adsorption index = ~EX1/~EX = ~EX1/(~EX1 +~EX2); where X = adsorbed amount/pulse; ~EX = adsorbed amount; when (X + B)/A 0.9, X = X1; when (X + B)/A less than 0.9, X = X2; A = amount of CO introduced/pulse = 0.002 mmol/pulse = 0.4 mmol/g-ruthenium/pulse; B = reversibly adsorbed amount.    USE -   For fuel cells, in particular solid macromolecular electrolyte fuel cells.    ADVANTAGE -   The method reduces the concentration of CO in hydrogen-containing gas prepared by reforming reaction of an organic compound, allowing the operation of fuel cells at low temperatures with high efficiency.    (JP10083825-A)      A production method for a hydrogen-containing gas for fuel cells comprises: (a) adding oxygen-containing gas to a hydrogen-containing gas containing carbon monoxide (CO), prepared by the reforming reaction of an organic compound, to give a mixed gas; and (b) bringing the mixed gas into contact with a catalyst composed mainly of ruthenium metal and having not less than 1 mmol/g-ruthenium CO adsorption and not less than 0.5 CO adsorption index, to oxidise and remove the CO. The CO adsorption index is given by: adsorption index = ~EX1/~EX = ~EX1/(~EX1 +~EX2); where X = adsorbed amount/pulse; ~EX = adsorbed amount; when (X + B)/A 0.9, X = X1; when (X + B)/A less than 0.9, X = X2; A = amount of CO introduced/pulse = 0.002 mmol/pulse = 0.4 mmol/g-ruthenium/pulse; B = reversibly adsorbed amount.    USE -   For fuel cells, in particular solid macromolecular electrolyte fuel cells.    ADVANTAGE -   The method reduces the concentration of CO in hydrogen-containing gas prepared by reforming reaction of an organic compound, allowing the operation of fuel cells at low temperatures with high efficiency.    (JP10212104-A)      A production method for a hydrogen-containing gas for fuel cells comprises: (a) adding oxygen-containing gas to a hydrogen-containing gas containing carbon monoxide (CO), prepared by the reforming reaction of an organic compound, to give a mixed gas; and (b) bringing the mixed gas into contact with a catalyst composed mainly of ruthenium metal and having not less than 1 mmol/g-ruthenium CO adsorption and not less than 0.5 CO adsorption index, to oxidise and remove the CO. The CO adsorption index is given by: adsorption index = ~EX1/~EX = ~EX1/(~EX1 +~EX2); where X = adsorbed amount/pulse; ~EX = adsorbed amount; when (X + B)/A 0.9, X = X1; when (X + B)/A less than 0.9, X = X2; A = amount of CO introduced/pulse = 0.002 mmol/pulse = 0.4 mmol/g-ruthenium/pulse; B = reversibly adsorbed amount.    USE -   For fuel cells, in particular solid macromolecular electrolyte fuel cells.    ADVANTAGE -   The method reduces the concentration of CO in hydrogen-containing gas prepared by reforming reaction of an organic compound, allowing the operation of fuel cells at low temperatures with high efficiency.    (US6190430-B1)      A production method for a hydrogen-containing gas for fuel cells comprises: (a) adding oxygen-containing gas to a hydrogen-containing gas containing carbon monoxide (CO), prepared by the reforming reaction of an organic compound, to give a mixed gas; and (b) bringing the mixed gas into contact with a catalyst composed mainly of ruthenium metal and having not less than 1 mmol/g-ruthenium CO adsorption and not less than 0.5 CO adsorption index, to oxidise and remove the CO. The CO adsorption index is given by: adsorption index = ~EX1/~EX = ~EX1/(~EX1 +~EX2); where X = adsorbed amount/pulse; ~EX = adsorbed amount; when (X + B)/A 0.9, X = X1; when (X + B)/A less than 0.9, X = X2; A = amount of CO introduced/pulse = 0.002 mmol/pulse = 0.4 mmol/g-ruthenium/pulse; B = reversibly adsorbed amount.    USE -   For fuel cells, in particular solid macromolecular electrolyte fuel cells.    ADVANTAGE -   The method reduces the concentration of CO in hydrogen-containing gas prepared by reforming reaction of an organic compound, allowing the operation of fuel cells at low temperatures with high efficiency.