Following the Money: Who Is on the Other Side

Take one trade, stylized but typical of the trades this chapter describes. Mid-morning on an ordinary weekday, a retail trader opens a brokerage app on a phone and buys one call option on the S&P 500 index (SPX) that expires at the close of trading that same afternoon. The strike is a few dozen points above the index. The screen shows the option at $5.00 a point, and because one SPX contract is worth $100 times the index, the trader is paying about $500 for the right to any rise above the strike in the next five or six hours. To the trader it is one decision about one number, the level of the S&P 500 at 4 pm.

Behind the screen, the order passes through at least five businesses, each of which is paid. The broker decides where to send it. Because SPX options are listed only on Cboe's exchanges, it goes to Cboe, where a market maker sells the call. The market maker immediately buys a small amount of S&P 500 exposure, in futures or in the SPY exchange-traded fund, so that it is not left holding a bet on the index. The trade is reported to the consolidated options tape and passed to the Options Clearing Corporation (OCC) in Chicago, which becomes the seller to the trader and the buyer to the market maker. At the close the option either expires worthless or is settled in cash, and by the evening nothing remains of it except the transfers it caused.

Multiply that trade by millions. Zero-days-to-expiry (0DTE) options, contracts traded on the day they expire, were a record 59% of SPX volume in 2025 and a record 66.2% in July 2026 (Cboe). Cboe's SPX options averaged about 3.9 million contracts a day in 2025, of which about 2.3 million were 0DTE (Cboe release, 6 Jan 2026). Across all US listed options, the OCC cleared 15,207,163,554 options contracts in 2025, up 24.4% from 12,224,227,606 in 2024 (OCC release, 5 Jan 2026), with a reported single-day record of about 110 million contracts on 10 October 2025 (secondary, attributed to OCC — verify). Each of those contracts had a buyer and a seller, and each was a transfer from one to the other, less what the intermediaries took.