CERCLA's text does not expressly impose joint and several liability, but courts have read it in by borrowing the common-law rule that defendants who cause a single, indivisible harm are each liable for the whole of it. Because contamination from multiple sources often commingles in soil or groundwater in a way that cannot be cleanly separated by source, courts have applied joint and several liability in the large majority of multi-party Superfund cases.

The Supreme Court's decision in Burlington Northern confirmed that a defendant can escape joint and several liability by proving the harm is reasonably capable of apportionment — for example, by volume, concentration, or geographic area of contamination — shifting the burden onto the defendant to establish a reasonable basis for divisibility. Where a party is held jointly and severally liable, its practical remedy is a contribution action against other PRPs to recoup their equitable share.

Joint and several exposure means a single deep-pocket PRP can bear the collection risk for an entire site even where its own contribution to the contamination was modest, which materially changes settlement incentives. A Juricratic simulation can model that asymmetry directly, letting a party dial its assumed share of the total plume against the risk of being the sole solvent defendant and see how that shifts the expected value of early settlement versus litigating divisibility.

Joint and several liability arguments surface most often in cost recovery actions naming a small number of well-capitalized defendants for contamination that in fact involves many historical contributors, prompting the named defendants to litigate divisibility as a liability-limiting defense and to file contribution claims to spread the ultimate cost.