The influence of surface tension, interfacial reaction, and solid surface properties on the spontaneous infiltration of porous SnO2 by liquid silver was investigated. It was found that infiltration is enhanced with higher oxygen concentration in the atmosphere. The role of additives was exemplarily addressed by utilizing small amounts of either WO3 or CuO. Attendant interfacial reactions were studied by simultaneous DSC/TG measurements. Furthermore, XPS measurements revealed the strong influence of SnO2 particle surface properties on infiltration. A non-stoichiometric surface was found to enhance the infiltration, whereas a stoichiometric SnO2 surface completely prohibits the infiltration by liquid Ag. This was additionally proven by changing the SnO2 surface properties through adding WO3 or CuO. WO3 as an additive stabilizes the stoichiometric SnO2 surface, and in contrast to this, CuO induces Sn2+ states. Thereby, spontaneous infiltration is prevented by WO3 and enhanced through CuO doping. The SnO2 infiltration behavior is explained by the interfacial interactions between Ag and the SnO2 surface.