Torts - Cases, Principles, and Institutions Fifth Edition, 2016a

Witt & Tani, TCPI 6. Causation
bioavailability than average would have caused less damage than its market share
would indicate.
Id. at 233. Are either of these distinctions persuasive?
4. Commingled products. After cases like Skipworth, some observers thought that market
share liability had no future. The giant litigation over a gasoline additive in the Southern District
of New York, however, suggested otherwise. Methyl tertiary butyl ether (“MTBE”) is a gasoline
additive that has been found leaking from underground storage tanks around the United States and
that has contaminated the water supply in many communities. Plaintiffs in a litigation before
Judge Shira Scheindlin could not identify the manufacturers of the MTBE responsible for the
chemical that had ended up in the Suffolk County, Long Island water supply. But Judge Sheindlin
allowed the plaintiffs to go ahead on what she called a “commingled product theory” that closely
resembles the market share theory:
[T]he commingled product theory, while still an alternative means of proving
causation, is closer to traditional causation than to market share liability. Under this
theory, a reasonable jury could conclude, based on the evidence in the record, that
all defendants contributed to the commingled gasoline that caused contamination in
plaintiffs’ wells. Defendants may still exculpate themselves by showing that their
product could not have been part of the commingled gasoline spilled in Suffolk
County, but the burden shifts to them to do so. . . .
A reasonable jury could conclude that most defendants’ gasoline contributed to
contamination in at least some of the wells at some point. To exempt defendants
from liability, when plaintiffs have proven the other elements of their claims, simply
because plaintiffs are unable to deconstruct the molecules of the commingled
gasoline to identify the manufacturers of each gallon of spilled gasoline is unjust.
To avoid such a result, New York courts have often “modif[ied] the rules of personal
injury liability, in order ‘to achieve the ends of justice in a more modern context’
and . . . to overcome ‘the inordinately difficult problems of proof caused by
contemporary products and marketing techniques.’” . . .
The commingled product theory lies somewhere between market share and
concurrent wrongdoing. It is similar to concurrent wrongdoing—a theory that
allows multiple tortfeasors to be held jointly and severally liable when each
tortfeasor’s independent actions combine to produce the same wrong—because it
addresses a situation in which multiple defendants have contributed to an indivisible
injury. It is similar to market share in that it shifts the burden to defendants to
exculpate themselves from liability.
The theory is different from market share liability, however, in an important way.
Market share liability was developed in the context of plaintiffs’ inability to identify
which manufacturer had produced the defective product-diethylstilbestrol (“DES”)
pills. Each plaintiff in the DES cases had ingested pills that were manufactured by
only one defendant, but no one could determine which of a small number of
manufacturers made those exact pills. When holding all manufacturers of the
generic pill liable under market share, courts recognized that all but one of them did
328