How Options Markets Work: Exchanges, the OCC, Market Makers, and Contract Adjustments

Listed options trade on regulated exchanges and are cleared by a central clearing house, which in the US is The Options Clearing Corporation (OCC). Exchanges match buyers and sellers, market makers supply continuous quotes, and OCC becomes the buyer to every seller and the seller to every buyer, guaranteeing that each contract is honored.

In short: in the US, more than a dozen options exchanges compete to trade the same standardized contracts, and OCC clears all of them, so a contract bought on one exchange can be sold on another. Market makers post bids and asks; brokers route customer orders to exchanges or market makers. OCC is the issuer and guarantor of every listed option and collects margin from its clearing members to back that guarantee. In Canada, listed options trade on the Montréal Exchange and clear through the Canadian Derivatives Clearing Corporation (CDCC). When a company splits its stock or pays a special dividend, the clearing house adjusts the options so holders and writers are treated fairly.

The misconception: “someone sold me this option, so they owe me”

When you buy an option, the person who sold it to you is effectively out of the picture once the trade clears. Your contract is with OCC. If you exercise, OCC assigns the exercise to some writer of that series, chosen through a random process, not to your original counterparty. And if a writer’s broker fails, OCC’s guarantee still stands behind the contract. This is the single biggest difference between a listed option and a private, over-the-counter contract.

A short history

The Chicago Board Options Exchange (now Cboe) opened on April 26, 1973, as the first US exchange for listed options, starting with calls on 16 stocks. The clearing house that became OCC was formed the same year; it is based in Chicago. Listed puts followed in 1977. Before then, options were negotiated one by one through dealers, with no standard strikes, dates, or guarantee.

Listed options have grown enormously since. OCC reported a record of roughly 15.2 billion US listed options contracts in 2025, and Cboe described 2025 as the sixth consecutive record year for US listed options volume.

The pieces of the market

Exchanges

US options trade on many exchanges, most of them owned by a handful of groups (including Cboe, Nasdaq, NYSE, and MIAX). They compete on fees, trading models, and speed. Because the contracts are standardized and all cleared by OCC, a Maple Widgets $50 call expiring December 18, 2026, is the same contract no matter which exchange it trades on.

Some products are exclusive to one exchange. SPX index options, for example, trade only on Cboe. Most stock and ETF options are multiply listed, trading on many exchanges at once.

Exchanges are linked, and rules generally prevent a trade from executing at a price worse than a better quote displayed on another exchange. The best bid and best offer across all exchanges is called the national best bid and offer (NBBO).

Market makers

Market makers are firms that commit to quoting bids and asks in the options they’re assigned to, for a minimum share of the trading day, under each exchange’s rules. They profit mainly from the spread between bid and ask, and they manage their risk by hedging, often by trading the underlying stock. Without them, you’d frequently find no one on the other side of an order in a less active strike. Their quotes are what you see in an options chain.

Brokers and order routing

Retail customers trade through brokers, who route orders to exchanges or, in some cases, to market-making firms. Some US brokers receive payment for order flow from the firms they route options orders to. SEC rules require brokers to disclose their routing practices publicly (under Rule 606 of Regulation NMS), so this is something you can look up for your broker.

OCC: the clearing house

OCC is the sole clearing agency for US exchange-listed equity options. It:

Issues and guarantees every listed option. After a trade, OCC stands between the two sides.
Works through clearing members. OCC deals only with its clearing members (large brokers and trading firms, more than 100 of them). Your broker either is a clearing member or uses one.
Collects margin and a clearing fund from clearing members, so it can cover a member’s default.
Processes exercises and assignments, including automatic exercise at expiration for options $0.01 or more in the money. The details are in how exercise and assignment work.
Publishes the Options Disclosure Document, Characteristics and Risks of Standardized Options, which US brokers must give customers at or before approval for options trading.

In July 2012, the Financial Stability Oversight Council designated OCC a systemically important financial market utility under the Dodd-Frank Act. It is overseen by the SEC, the CFTC (for futures it clears), and the Federal Reserve. Regulation of the whole system is covered in how options markets are regulated.

How a trade flows

You enter an order with your broker to buy one Maple $50 call at a limit of $1.85.
Your broker routes it to an exchange (or a market maker).
It matches with a seller, perhaps a market maker, perhaps another customer.
The trade is reported, and each side’s clearing member submits it to OCC.
OCC becomes the counterparty to both. You hold a long call; the seller holds a short call; OCC guarantees both.
Cash for the premium settles the next business day, and the position appears in your account.

If you later sell the call, OCC simply closes your position. If the original seller later buys it back, theirs is closed too. The two of you never need to interact.

In Canada: the Montréal Exchange and CDCC

Canada has one options exchange for listed equity and index options: the Montréal Exchange (MX), owned by TMX Group. Its options are cleared by the Canadian Derivatives Clearing Corporation (CDCC), also part of TMX, which is the issuer, clearing house, and guarantor of the contracts, playing the role OCC plays in the US. Like OCC, CDCC publishes a disclosure document on the characteristics and risks of the options it clears.

Key features of MX equity options:

100 shares per contract, American style, physically settled.
Monthly expiries on the third Friday, with weekly options on some classes.
Index options on the S&P/TSX 60 (SXO) are European style and cash settled.

MX is recognized and supervised by Quebec’s securities regulator, the Autorité des marchés financiers (AMF). The dealers you trade through are regulated by the Canadian Investment Regulatory Organization (CIRO). Many Canadians also trade US-listed options through Canadian brokers; those contracts are cleared by OCC.

Contract adjustments: when the company changes

Options are written on a specific deliverable, usually 100 shares. When a company does something that changes what a share is worth or what a shareholder holds, the clearing house adjusts the contract so the option isn’t unfairly helped or hurt. At OCC, adjustments are decided case by case by an adjustment panel that includes representatives of OCC and the exchanges, following OCC’s By-Laws, and announced through OCC information memos.

Stock splits

2-for-1 split: one $50 call on 100 shares becomes two $25 calls on 100 shares each. You held the right to buy 100 shares for $5,000; you now hold the right to buy 200 shares for $5,000. Nothing has changed in value.
3-for-2 split: the strike stays the same and the deliverable changes. A $50 call on 100 shares becomes a $50 call on 150 shares. It now trades as a non-standard, adjusted option with its own symbol.
Reverse split: in OCC’s example, a 3-for-4 reverse split turns a $50 option on 100 shares into one on 75 shares.

Special dividends

Ordinary, regularly scheduled cash dividends do not trigger adjustments; option prices already reflect them. A special (non-ordinary) cash dividend can, if it is at least $12.50 per contract (equivalent to $0.125 per share on a standard 100-share contract), per OCC’s current rules. The usual method is to reduce the strike by the dividend amount.

A dated example: when Costco paid a $15 special dividend in December 2023, OCC (in Information Memo #53778) adjusted Costco options effective the December 27, 2023 ex-date by lowering every strike by $15. A $600 call became a $585 call. The holder lost $15 per share in stock value on the ex-date but gained $15 per share through the lower strike, leaving them roughly where they were.

Mergers, spin-offs, and other events

In a merger, the deliverable typically becomes whatever shareholders receive: shares of the acquirer, cash, or a mix. After a spin-off, the deliverable can become 100 shares of the parent plus some number of shares in the new company. These adjusted contracts can behave very differently from regular options, and their chains can be confusing.

In Canada, CDCC and the Montréal Exchange publish adjustment notices for affected classes in the same spirit.

What can go wrong

Trading an adjusted option by accident. An adjusted contract can sit right next to a regular one in a chain with a different deliverable. Always check the deliverable before trading a strange-looking price.
Assuming you know your counterparty. You don’t, and assignment is random.
Poor routing and wide spreads. Execution quality varies by broker and by contract.
Broker-level risk. OCC guarantees the contract to clearing members, but your relationship is with your broker. Investor protection schemes such as SIPC in the US and CIPF in Canada cover customer assets if a member firm fails, within limits; they do not protect against trading losses.
Event surprises. A takeover announcement or special dividend can change an option’s terms and value overnight.

The takeaway

Options markets combine competing exchanges, market makers supplying quotes, brokers routing orders, and a central clearing house that issues and guarantees every contract: OCC in the US, CDCC in Canada. That structure is what makes options standardized, interchangeable, and backed by more than the promise of a single seller. When a company splits its shares or pays a special dividend, the clearing house adjusts the contracts so neither side gains or loses from the change itself.