Abstract: The aim of this article is to compare strict liability and negligence rules on the basis of the incentives the provide to "appropriately" reduce accident losses. It will therefore be both convenient and clarifying to abstract from other issues in respect to which the rules could be evaluated. In particular, there will be no concern with the bearing of risk - for parties will be presumed risk neutral - nor with the size of "administrative costs" - for the legal system will be assumed to operate free of such costs - nor with distributional equity - for the welfare criterion will be taken to be the following aggregate: the benefits derived by parties from engaging activities less total accident losses less total accident prevention costs.