This paper aims to contribute to our understanding of financial reporting issues related to environmental liabilities in two ways. First, we investigate whether characteristics known at various points in a Federal Superfund site’s regulatory history are significant in explaining cleanup cost estimates. We analyze cost estimates because actual cleanup costs generally are not known; at most sites cleanup is incomplete and there is no central tracking of cleanup costs. We estimate the relation between engineering cost estimates and site characteristics known prior to the availability of these estimates, and use this model to estimate cleanup costs for sites without cost estimates. We base measures of firms’ environmental liabilities on these estimates.