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  1. If I am correct, dealers purchase assets for their own accounts, and later sell them for a profit from their inventory. But the spreads is the difference between buy (or "bid") prices and sell (or "ask") prices at the same time. So how can dealers earn the bid-ask spread?

  2. From Investopedia's Bid-Ask Spread page:

    The size of the spread from one asset to another will differ mainly because of the difference in liquidity of each asset.

    Since the spread is taken away by the dealers, how can it represent the difference in liquidity of the two assets?

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3 Answers 3

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  1. Market-makers (which you term dealers) earn the bid-ask spread by buying and selling in as short a window as possible, hopefully before the prices have moved too much. It is not riskless. The spread is actually compensation for this risk. From The Race to Zero:

    The market-maker faces two types of problem. One is an inventory-management problem – how much stock to hold and at what price to buy and sell. The market-maker earns a bid-ask spread in return for solving this problem since they bear the risk that their inventory loses value.

    Market-makers face a second, information-management problem. This arises from the possibility of trading with someone better informed about true prices than themselves – an adverse selection risk. Again, the market-maker earns a bid-ask spread to protect against this informational risk.

    The bid-ask spread, then, is the market-makers’ insurance premium. It provides protection against risks from a depreciating or mis-priced inventory. As such, it also proxies the “liquidity” of the market – that is, its ability to absorb buy and sell orders and execute them without an impact on price. A wider bid-ask spread implies greater risk in the sense of the market’s ability to absorb volume without affecting prices.

  2. The less liquid an asset is, the more time is likely to pass (and hence more information likely to arrive) until someone comes along to take the inventory from the dealer, and the greater is the risk that the price will have changed in the mean time. Since spread is compensation for this risk, ceteris paribus spreads are wider for less liquid assets.

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  • Thanks! (1) How is spread compensation for the risk? (2) What does "information" mean in "more information likely to arrive"?
    – Tim
    Sep 21, 2011 at 16:04
  • (3) Are market-makers same as dealers? (note that I just learned the difference between brokers and dealers.) Do they actually make the markets?
    – Tim
    Sep 21, 2011 at 16:14
  • @Tim (3) Dealers typically serve a market-making function (though sometimes they are dealing in products which they also originate), and certainly not all market makers are dealers. Your statement regarding spreads applies to dealers doing market-making, and also non-dealer market-makers.
    – Tal Fishman
    Sep 21, 2011 at 16:41
  • @Tim Not sure what is your question about (1), seems pretty clear to me. (2) Information is deliberately vague, could be anything which moves the price.
    – Tal Fishman
    Sep 21, 2011 at 16:43
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    The discussion linked above in the chat room is well worth the read, particularly: "MMs are offering to trade, at either price, the risk is that all the orders will be in one direction and then prices will move. A trade is completed when someone "hits" a MM bid or "lifts" a MM offer. Then the MM gains or loses inventory. As the inventory is accumulated, there is a risk that the prices move such that the MM is unable to load the inventory at a better price than which it was acquired."
    – MarkWayne
    Feb 8, 2019 at 20:24
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Every merchant makes money by buying wholesale, and selling retail. In the case of a market maker, the "bid" is the "wholesale" price, and the "ask" is the retail price.

In "real life," the difference between wholesale and retail depends on how quickly something sells. High volume items like gasoline and milk have narrow spreads between wholesale and retail because they sell quickly. Low volume items like furniture and cars sell slowly, and thus have much larger spreads. The same is true for high and low volume stocks.

In the case of IBM, the bid-asked spread might be a penny (or less). If the dealer can buy-sell one million shares of IBM, he'll make 1 million pennies, or $10,000, in a short period of time. Other stocks trade only a few thousand shares a day. In that case, the spread might be five, ten cents or even more, just to make it worthwhile for the dealer to trade them.

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  • 'the "bid" is the "wholesale" price, and the "ask" is the retail price' -- this is true in rising market. When prices are falling, the reverse holds. An important point, not explained here, is that that the bid-ask spread is the average that a competent (error-free) market maker can expect to make in their dealings. Sometimes they make more (in large volume events the spread can get big) and sometimes less (if the price moves quickly away from a region in an impulsive move they can be stuck holding positions/inventory that was traded far from the now current price).
    – MarkWayne
    Feb 8, 2019 at 20:32
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Market makers make the spread on market orders, only. A market order is one in which the retail buyer/seller says fill the order immediately at whatever is the best price. The market maker is buying the market-sells at the bid and selling the market-buys at the ask. If the market-buy volume equals the market-sell volume then the market maker is just transferring shares between market-buyers and market-sellers and pocketing the the bid-ask spread (in addition to commissions.) Limit-buy orders are filled when limit-sellers drop their asking price and limit-sell orders are filled when limit-buyers raise their bid. The market maker makes only commission on limit orders but limit orders define the bid-ask spread.

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  • Welcome to Personal Finance & Money! While it's normally a bit weird to answer an already answered question from 3 years ago, in this case I think your answer is better than either of the other two. But it still has some errors that prevent me from upvoting it. Perhaps I'm just nitpicking semantics, but it is not the case that market orders are the only kind of orders that cross the spread; you can certainly send a limit buy at the current ask while the rest of the bid side of the market stays where it is. This looks like a market order but is not the same thing.
    – dg99
    Nov 21, 2014 at 18:19
  • Yes, the market maker pockets the bid-ask differential if he's on both sides of the trade but he's not receiving a commission. That goes to the broker if it's one that charges commissions.
    – Bob Baerker
    Jun 30, 2021 at 19:21

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