PRODUCT LIABILITY | 2026-09-30
Market Share Liability in California: Suing When You Cannot Identify the Manufacturer
California created a landmark rule for cases where a defective product cannot be traced to a single maker: under Sindell v. Abbott Laboratories, manufacturers can be liable in proportion to their share of the market.
A basic requirement of a product-liability claim is proving <strong>which manufacturer</strong> made the product that caused the harm. But some products are <strong>fungible</strong> — identical across many makers — and injuries can surface years or decades later, long after the specific product and
When a harmful product cannot be traced to one company, ordinary causation rules would leave a blameless plaintiff with no remedy. Sindell created a limited path to recovery.
The Identification Problem
Traditional product-liability law requires the plaintiff to prove that a specific defendant made the product that injured them. For fungible products made identically by many manufacturers — and where injury manifests long after use — that proof can be impossible. The classic example is DES (diethylstilbestrol), a drug taken by pregnant women that caused injuries in their daughters years later, by which time the specific manufacturer often could not be identified. Sindell arose from exactly this scenario.
Sindell v. Abbott Laboratories
In Sindell, the California Supreme Court crafted market share liability to prevent innocent plaintiffs from being denied recovery merely because they could not identify which of several identical-product makers caused the harm. Under the theory, where the plaintiff joins the manufacturers of a substantial share of the relevant market, each defendant can be held liable for a percentage of the plaintiff’s damages equal to its share of that market — unless a defendant proves it could not have made the product that injured the plaintiff. The burden of apportionment shifts in a way that reflects each maker’s contribution to the risk.
Requirements of the Theory
Market share liability is narrow. Courts have generally looked for conditions such as:
- the product was fungible — essentially identical across manufacturers, produced from a common formula or design;
- the plaintiff, through no fault of their own, cannot identify the specific manufacturer;
- the plaintiff joins manufacturers representing a substantial share of the relevant market; and
- the injury was caused by the product’s defect common to all the makers.
Where these conditions are absent — for example, where products differ meaningfully among makers, or the specific manufacturer can be identified — the theory does not apply.
Apportionment by Market Share
The defining feature of the doctrine is that liability is apportioned by market share rather than imposed jointly for the entire loss. Each manufacturer answers for the portion of damages corresponding to its share of the relevant market, aligning responsibility with the probability that a given maker’s product caused the harm. A defendant that demonstrates it could not have produced the specific product at issue may be exonerated.
Limits: Brown v. Superior Court and Beyond
California later clarified the boundaries of the doctrine. In Brown v. Superior Court, the Court addressed the application of market share liability in the DES context and confirmed that liability under the theory is several — each defendant is responsible for its market-share portion, not the entire judgment. Courts have also been cautious about extending the theory beyond truly fungible products; it has generally not been applied to products that vary in design or risk among manufacturers. The doctrine remains an exception crafted for a specific problem, not a general substitute for proving causation.
Why It Matters
Market share liability is significant for two reasons. It ensures that a plaintiff harmed by a fungible product is not left remediless simply because time and circumstance erased the trail to a single manufacturer. And it allocates responsibility fairly among the makers who collectively created the risk. For plaintiffs, the key questions are whether the product is truly fungible and whether a substantial share of the market can be brought before the court; for manufacturers, whether they can prove non-involvement or defeat the theory’s prerequisites.
Frequently Asked Questions
What is market share liability?
A theory allowing recovery against manufacturers of a fungible product in proportion to their market shares when the specific manufacturer cannot be identified.
What case created it?
Sindell v. Abbott Laboratories, a California Supreme Court decision arising from DES injuries.
When does it apply?
Generally when the product is fungible, the plaintiff cannot identify the maker through no fault of their own, and a substantial share of the market is joined.
How is liability divided?
By market share — each manufacturer is liable for the percentage of damages equal to its share of the relevant market, on a several basis.
Can a manufacturer avoid liability?
Yes — a defendant that proves it could not have made the product that injured the plaintiff may be exonerated.
Does it apply to all products?
No — it is generally limited to truly fungible products and has not been extended to products that differ in design or risk among makers.
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Talk to a California Product Liability Attorney
If a fungible product harmed you and the maker cannot be identified, market share liability may still allow recovery. Trembach Law Firm evaluates California product-liability claims. Call (818) 514-7680.
Contact Trembach Law Firm at (818) 514-7680 for a confidential consultation.
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