The effects of additives in n-type semiconducting SnO$_2$-based gas sensors on oxidizing gases were investigated. The resistivity of SnO$_2$ sensors decreased when exposed to reducing gases, which act as electronic donors. However, the resistivities of the SnO$_2$ sensors increased when exposed to oxidizing gases, which act as electronic accepters. The products formed from the reaction of oxidizing gases ever SnO$_2$-based powders were analyzed by gas chromatography as compared with those formed from the reaction of reducing gases of alcohols. The SnO$_2$ sensors doped with PdCl$_2$ or A1$_2$O$_3$ showed unique dual response patterns toward oxidizing gases of $CH_3$CN and $CH_3$NO$_2$ depending on the operating temperature. The combination of these two sensors along with proper pattern recognition technique could enhance the selectivity for the gases with electron-accepting groups.