2026-07-09http://hdl.handle.net/123456789/594103One challenge in environmental liability law is to apportion the liability appropriately among multiple parties, when these multiple parties generate a single and non-separable damage. This paper provides a method of designing efficient apportionment rule in the presence of product market competition. In particular, I examine the role of apportionment rule in inducing abatement technology diffusion between competing firms. I show that such diffusion can be induced by an efficient apportionment rule. And this apportionment rule allocates a relatively large (more than 1/2) portion of the liability to the firm which originally owns the abatement technology. Furthermore, allocating the liability equally between the firms cannot induce diffusion.Text