Characterization of efficient simple liability rules with multiple tortfeasors

The paper considers the efficiency of simple liability rules when there are multiple injurers. It is shown that a necessary and sufficient condition for any simple liability rule to be efficient is that it satisfy the condition of collective negligence liability. The condition of collective negligence liability, introduced in this paper, requires that whenever some individuals are negligent, no nonnegligent individual bears any loss in case of occurrence of accident.