AbstractA growing body of literature suggests that courts and juries are inclined toward division of liability between two strictly non-negligent or “vigilant” parties. In this paper, we explore the economic efficiency of liability rules based on comparative vigilance. We devise rules that are efficient and that reward vigilance. Commonly used liability rules have discontinuous liability shares. We develop a liability rule, which we call the “super-symmetric rule,” that is both efficient and continuous, that is based on comparative negligence when both parties are negligent and on comparative vigilance when both parties are vigilant, and that is always responsive to increased care.