On what grounds did Lot expect to be saved if he went to Tzo'ar?
Rashi #1 and Targum Yonasan: He hoped that Tzo'ar would be spared, because, since it was built one year after S'dom, its sins were fewer than those of S'dom.
Rashi #2 Targum Onkelos and Rashbam: Because it was smaller than S'dom, and Hashem might agree to spare it to enable him to escape there. 1
The two explanations argue about whether "Mitz'ar" means 'younger' (in years) or 'fewer' (in inhabitants).