What Is the Sherman Antitrust Act and How Does It Work?

The Sherman Antitrust Act is the 1890 federal law that makes it illegal for competing businesses to rig markets through agreements like price-fixing, and illegal for a single company to monopolize an industry through predatory tactics.¹ Codified at 15 U.S.C. §§ 1–3, the statute has three sections: the first covers anticompetitive agreements between separate companies, the second covers monopolistic conduct by individual firms, and the third extends both prohibitions to U.S. territories and the District of Columbia. Violations are federal felonies carrying fines up to $100 million for corporations and up to 10 years in prison for individuals, and the same conduct exposes companies to private lawsuits where damages are automatically tripled.

Agreements Between Competitors (Section 1)

Section 1 makes it a felony to enter into any agreement that unreasonably restricts trade or commerce between states or with foreign countries.² The word “unreasonably” matters. Since 1911, the Supreme Court has read the statute to reach only agreements that limit competition without legitimate justification, not every arrangement that technically reduces rivalry.³ Forming a business partnership eliminates some competition between the partners, but that alone is not a violation.

What Section 1 requires is an actual agreement between two or more separate parties. A company acting on its own cannot violate this section, even if its behavior hurts competitors. The government or a private plaintiff has to prove that distinct actors coordinated. That coordination usually takes one of three forms:

Price-fixing, where competitors agree on what to charge rather than setting prices independently.
Market allocation, where companies divide territories or customer groups so they avoid competing.
Bid-rigging, where firms coordinate their bids on contracts so a pre-selected company wins.

These three account for the bulk of criminal prosecutions under the statute. They are harmful because they replace independent decisions with collective control over prices, output, or market access.

Monopolization by a Single Firm (Section 2)

Section 2 shifts the focus from group behavior to individual firms. It makes it a felony to monopolize, attempt to monopolize, or conspire to monopolize any part of interstate or foreign commerce.⁴ A monopolization claim has two parts. The company must hold monopoly power in a defined market, and it must have acquired or maintained that power through anticompetitive conduct rather than by offering a better product or running a more efficient operation.

Being big is not the problem. A company that dominates because customers genuinely prefer its product has not violated anything. Section 2 targets firms that use their dominance to shut competition down, through tactics like predatory pricing (selling below cost temporarily to bankrupt smaller rivals) or exclusive dealing arrangements designed to lock competitors out of distribution channels.

Defining the “relevant market” is often the most contested issue. Courts look at which products consumers treat as interchangeable and the geographic area where competition actually occurs. A firm might have a small share of a broadly defined market but a stranglehold on a narrowly defined one, and which definition the court adopts frequently decides whether monopoly power exists at all.

How Courts Judge Conduct

Not all anticompetitive behavior gets the same scrutiny. Courts use two frameworks, and the choice between them often decides the outcome.

Per Se Violations

Some conduct is treated as automatically illegal. Price-fixing, bid-rigging, and market allocation among competitors fall into this category.⁵ Under the per se standard, a plaintiff does not need to prove that the agreement actually harmed competition or that the participants intended harm. The agreement itself is enough. Courts skip the detailed economic analysis because decades of experience have shown these arrangements virtually never produce legitimate benefits.

Rule of Reason

Everything else gets evaluated under the rule of reason, a more flexible test that weighs a practice’s pro-competitive benefits against its anticompetitive effects.⁵ Courts examine the structure of the industry, the market power of the parties, and whether the restriction reduces competition or just changes how it operates. A joint venture between two manufacturers that limits each partner’s sales might look restrictive on paper but could promote efficiency or bring a product to market that neither company could develop alone. The rule of reason is built to distinguish those situations from genuine anticompetitive harm.

Criminal Penalties

Every section of the Sherman Act creates felony liability. Congress raised the penalty caps substantially in 2004, and the current maximums reflect that increase.⁶²⁴⁷ Courts may impose fines above these caps when the defendant gained more than $100 million from the violation, using a formula tied to the actual gains or losses involved.

In practice, criminal prosecutions concentrate on Section 1 conspiracies, particularly price-fixing and bid-rigging, because those are the clearest cases of intentional wrongdoing.⁵

Private Lawsuits and Treble Damages

Criminal prosecution is only half the picture. Under the Clayton Act’s damages provision, which applies to Sherman Act violations, anyone injured in their business or property by illegal anticompetitive conduct can sue in federal court and recover three times their actual losses, plus attorney’s fees and court costs.⁸ The automatic tripling compensates victims more fully, since proving the exact extent of antitrust harm is notoriously difficult, and it gives private parties a strong financial incentive to sue. Most antitrust cases in the United States are in fact filed by businesses and individuals, not the government.⁹

Private parties can also seek injunctions to stop anticompetitive conduct before it causes further damage. A plaintiff who substantially prevails in an injunction action can recover the cost of the lawsuit, including reasonable attorney’s fees.¹⁰

The deadline is short. Private damage claims must be filed within four years after the cause of action arises, and missing the deadline bars the claim permanently.¹¹ Because cartels are often hidden, the clock may not start until the plaintiff discovers or reasonably should have discovered the violation.

Who Enforces the Sherman Act

Two federal agencies share antitrust enforcement, but their roles differ. The Department of Justice Antitrust Division is the only agency that can bring criminal charges under the Sherman Act.⁹ It investigates suspected cartels, prosecutes individuals and corporations, and can seek prison sentences.

The Federal Trade Commission enforces competition law under the FTC Act, which the Supreme Court has said reaches the same conduct the Sherman Act prohibits. The FTC does not technically enforce the Sherman Act directly, but it brings civil cases targeting the same anticompetitive behavior and refers evidence of criminal violations to the DOJ.⁵

Key Exemptions

Not every form of collective economic activity is covered. Several significant exemptions have been carved out over the years.

The Clayton Act provides that labor unions, agricultural cooperatives, and horticultural organizations formed for mutual benefit are not illegal combinations under the antitrust laws.¹² Without this exemption, workers collectively bargaining for wages would technically be fixing the price of labor.

The McCarran-Ferguson Act limits Sherman Act coverage of the insurance industry to areas that state law does not already regulate.¹³ Because most states heavily regulate insurance, this historically provided broad protection. Congress narrowed the exemption in 2021 for health and dental insurers, making them subject to federal antitrust enforcement for practices like price-fixing. Even under McCarran-Ferguson, the exemption has never protected agreements to boycott or coerce.

Narrower carve-outs exist for certain export trade associations, professional baseball (a judicially created anomaly), and specific activities authorized by federal regulatory agencies. These protect defined activities, not entire industries.

Conduct Outside the United States

The Sherman Act does not stop at the border, and it does not reach all foreign conduct either. Under the Foreign Trade Antitrust Improvements Act, the statute covers overseas conduct only when that conduct has a direct, substantial, and reasonably foreseeable effect on U.S. domestic commerce or on the export business of a U.S. company.¹⁴ A foreign price-fixing cartel that inflates prices paid by American consumers falls within the Act’s reach even though the agreement was made overseas. A cartel that only affects prices in foreign markets generally does not.

The Leniency Program

One of the most effective tools for uncovering cartels is a deal. The Antitrust Division runs a leniency program offering non-prosecution protection to the first company that reports its participation in a price-fixing, bid-rigging, or market allocation conspiracy.¹⁵ The program has operated since the early 1990s and has been responsible for cracking some of the largest international cartels.

To qualify, a company must be the first to come forward, must end its participation in the illegal activity, must cooperate fully and candidly with the investigation, and must not have been the ringleader of the conspiracy. Individuals can also apply for leniency on their own behalf under a separate policy. The first participant to report gets protection; everyone else faces the full weight of criminal prosecution. That structure creates a race to the government’s door once any conspirator suspects the scheme might unravel.

1
National Archives. Sherman Anti-Trust Act (1890)
2
Office of the Law Revision Counsel. 15 USC 1 – Trusts, Etc., in Restraint of Trade Illegal; Penalty
3
Justia. Standard Oil Co. of New Jersey v. United States, 221 U.S. 1 (1911)
4
Office of the Law Revision Counsel. 15 USC 2 – Monopolizing Trade a Felony; Penalty
5
Federal Trade Commission. The Antitrust Laws
6
Department of Justice. Antitrust Criminal Penalty Enhancement and Reform Act of 2004
7
Office of the Law Revision Counsel. 15 USC 3 – Trusts in Territories or District of Columbia Illegal; Combination a Felony
8
Office of the Law Revision Counsel. 15 USC 15 – Suits by Persons Injured
9
Federal Trade Commission. Guide to Antitrust Laws – The Enforcers
10
Office of the Law Revision Counsel. 15 US Code 26 – Injunctive Relief for Private Parties; Exception; Costs
11
Office of the Law Revision Counsel. 15 US Code 15b – Limitation of Actions
12
Office of the Law Revision Counsel. 15 USC 17 – Antitrust Laws Not Applicable to Labor Organizations
13
Office of the Law Revision Counsel. 15 USC 1012 – Regulation by State Law; Federal Law Relating Specifically to Insurance
14
Office of the Law Revision Counsel. 15 USC 6a – Conduct Involving Trade or Commerce With Foreign Nations
15
Department of Justice. Antitrust Division Leniency Policy