Hydrogen can be generated from formic acid in aq. phase homogeneous catalytic reactions using ruthenium catalysts with water-sol. phosphine ligands. A comparison of tri-, di-, and mono-sulfonato triphenylphosphine, disulfonato diphenyl-alkyl-phosphines (Ph2PR; R=Me, n-Bu, Cyp), and monosulfonato phenyl-dialkyl-phosphines (PhPR2; R=Me, Cyp) is described. Using two equiv. of water-sol. phosphine per ruthenium ion, significant turnover frequencies are obsd. for the decompn. of formic acid. The influence of basicity, water soly. (related to the structures and behavior in aq. soln.), electronic properties, and steric effects of the phosphines on the rate of the hydrogen generation are investigated.