Ultra thin Pd films (5-30nm) deposited by RF sputtering have shown fast and detectable responses for low concentrations of H2 gas(0.3-4%) and compounds containing hydrogen such as ammonia, methanol (~1OOppm mixtures in air) at different temperatures. These films have been characterized in dynamic temperature programmed and static conditions for 100-300 "C range, in air with respect to their resistivity. The electrical resistivity of Pd films gets modified on exposure to such gas mixtures and measured changes are reported. The observed changes in resistivity on exposure to above gas mixtures are much  larger (more then by an order) then earlier reported results in literature.