The book is the product
A bookmaker's product is a price. A prediction market's product is a place where prices happen. That inversion changes what the business has to be good at. A sportsbook employs traders to be right about probabilities; an exchange employs nobody to have a view and instead has to attract enough people with views, and enough capital willing to quote, that the book is deep at the moments customers want to trade.
The metric that captures this is not margin but liquidity: how much can be traded at or near the current price without moving it. A market with a hundred dollars on the bid and a hundred on the offer at a one-cent spread is a good market for a customer wanting to trade fifty dollars and a useless one for a customer wanting to trade five thousand. Every conversation about whether prediction markets can compete with sportsbooks is, underneath, a conversation about liquidity.
Makers, takers and the fee
Exchanges charge fees per trade, and the convention in this product, borrowed from equities and crypto, is to charge differently for the two roles.
A maker posts a limit order that rests in the book: buy yes at 62, say, when the best offer is 64. A taker hits an order already in the book, accepting the price on offer. Makers provide liquidity; takers consume it. Venues typically charge takers a fee and charge makers little or nothing, and some pay makers a rebate, because without resting orders there is nothing for anyone to take.
The fee is usually expressed as a function of the contract price rather than a flat percentage, because a flat fee on a contract at 95 cents would be a huge fraction of the possible profit and a trivial fraction on one at 50 cents. A common formula charges a percentage of the product of the price and one minus the price, which is highest at 50 cents and falls to near zero at the extremes. On a contract at 50 cents that formula produces a cost in the region of one to two cents per contract, a total round-trip cost well below the margin in a typical sportsbook line. That gap is the customer's advantage and the venue's problem: it earns a fraction of what a bookmaker earns on the same wager.
Who quotes
Retail customers rarely post resting orders at both sides of a market. Liquidity comes from three sources.
Designated market makers. Professional trading firms contracted by the venue, typically under a programme that rebates fees or pays for meeting quoting obligations, to maintain two-sided quotes within a maximum spread for a minimum share of the trading day. In the regulated American venues these are the same kinds of firms that make markets in options and crypto, and the largest have taken equity stakes in the venues they quote on.
Informed participants. Traders with a model, an edge or information, who post orders at prices they believe are right and are happy to be filled. On sports contracts this population overlaps almost entirely with the sharp bettors a sportsbook would limit or ban. On an exchange they are welcome, because they are the ones keeping the price honest and the venue earns a fee whether they win or lose.
Hedgers. A bookmaker, a syndicate or a media company with exposure to an outcome can offset it on an exchange, and the deepest markets in any sport are the ones where that hedging flow exists. This is the reason exchanges want sportsbook partners: the partner's liability becomes the exchange's liquidity.
The consequence for market quality is a familiar one from betting exchanges. Mainstream events with public interest and professional flow are liquid, tight and well priced. Niche events are thin, and a customer who wants to trade them pays a wide spread or does not get filled. An exchange cannot offer three thousand markets a day at usable prices the way a bookmaker's pricing engine can, because it has to persuade someone to take the other side of each of them.
How the price moves
Prices move on an exchange for the same reasons odds move at a bookmaker: new information, flow and the correction of errors. The mechanics differ.
On an exchange, a large buy order walks up the book, filling the best offers first and moving the last-traded price. If the order was informed, the new price is more accurate; if it was a large retail order without information, the price has moved for no reason and market makers will sell into it until it comes back. The public can watch this happen in the order book, which is a level of transparency no bookmaker offers.
Two systematic patterns are worth knowing. The favourite-longshot bias, well documented in betting, appears in prediction markets too: contracts at very low prices tend to be overpriced, because a few cents feels cheap for a chance at a dollar, and contracts at very high prices tend to be slightly underpriced, because the profit looks small. Market makers who understand this quote accordingly. And thin-book drift: in a market with little liquidity, the price is whatever the last small trade was, and it can sit far from the true probability for hours. Reading a two-dollar trade as "the market thinks" is a mistake the press makes constantly.
Resolution sets the price at the end
Every contract has a resolution rule: the source that will be consulted, the time at which it will be consulted and what counts as yes. The price converges toward one dollar or zero as the event approaches and the outcome becomes clear, and it settles at the rule's answer.
The quality of the rule matters more than it sounds. A contract on "will the Federal Reserve cut rates in March" is easy to write. A contract on "will a ceasefire be agreed by the end of the month" is not, because reasonable people can disagree about what happened, and a market that resolves on a contested reading of events destroys trust in every other market on the venue. Regulated exchanges resolve through an internal process with published criteria and an appeal route; crypto-native venues resolve through an oracle in which token holders vote, a process that has been gamed. Lesson four returns to this.
What the venue earns
Put the pieces together and the exchange's economics are visible. Revenue is the fee on volume: a small number of cents per contract, weighted toward contracts near 50 cents and toward takers. Cost is technology, compliance, market-maker incentives, marketing and, for the regulated venues, the substantial cost of being a federally supervised exchange.
The number that matters is volume, and the venues report it because it is the number that grows. A billion dollars of monthly notional at a blended fee of one per cent is ten million dollars of revenue, which is a small sportsbook. The largest venues crossed that scale in 2025 on the strength of sports contracts, and the reason sports matter to them is the same reason sports matter to bookmakers: it is the only category with daily, repeatable, mainstream demand.
The customer's arithmetic
A bettor comparing an exchange to a book should compare total cost, and the honest comparison is closer than the headline. A sportsbook's margin on a two-way market is typically four to five per cent of stake; on player props and same-game parlays it can be several times that. An exchange charges a fee that is usually under two per cent, but the customer also crosses a spread, which on a liquid market is a cent or two and on an illiquid one can be ten. For a mainstream game the exchange is cheaper. For an obscure prop it may not be, and it may not be available at all.
The other difference is limits. A sportsbook restricts customers who win; an exchange does not care who wins because it is not the counterparty. For a sharp bettor that is decisive, and it is why the professional money moved to exchanges as soon as sports contracts were listed. Whether that money's presence makes the exchange a better or worse place for a recreational customer is a question lesson five takes up.
What to take from this lesson
An exchange earns less per wager than a bookmaker and needs more of them. Its quality depends on liquidity, which depends on market makers and hedgers, which depends on partnerships. Its prices are transparent and, in liquid markets, more accurate than a bookmaker's, because the sharpest participants are welcome rather than limited. Its weaknesses are the mirror image: thin markets, wide spreads on anything niche and a resolution process that has to be trusted. Every strategic decision about this product is a decision about which of those facts dominates.