Javier Mendoza 
A one-cent bid-ask spread can make a market look incredibly liquid. Then an unexpected economic announcement arrives, volatility explodes, and that same spread suddenly becomes five, ten, or twenty times wider.
The asset itself has not disappeared. What changed is the willingness of buyers and sellers – especially professional liquidity providers – to quote aggressively around the current market price.
That is why bid-ask spread dynamics across different liquidity regimes deserve more attention than they usually receive.
The spread is simply the difference between the highest available bid and the lowest available ask. The SEC describes these as the highest price buyers are willing to pay and the lowest price sellers are willing to accept.
But that small number contains a surprising amount of information. Spreads reflect liquidity, volatility, market-maker risk, competition, trading activity, and available depth.
Understanding how they change between calm, active, and stressed environments can help traders estimate execution costs before those costs become painfully obvious.
Start With What the Bid-Ask Spread Represents
Suppose a stock shows:
Bid: $49.99
Ask: $50.01
The quoted spread is:
$50.01 − $49.99 = $0.02
A trader who immediately buys generally crosses toward the ask. Someone immediately selling normally trades toward the bid.
That spread therefore represents part of the cost of demanding immediate liquidity.
The SEC notes that narrower spreads are generally associated with more liquid markets, while wider spreads indicate a larger difference between the prices at which buyers and sellers are willing to transact.
Relative spread can also be useful:
Relative Spread = (Ask − Bid) ÷ Midpoint
A two-cent spread means something very different for a $1 stock than for a $1,000 asset.
For cross-market comparision, basis points or percentages are therefore usually more informative than raw dollar spreads.
Tight Spreads Usually Define High-Liquidity Regimes
Highly liquid markets typically have several characteristics working together.
Trading activity is strong, multiple market makers compete for orders, depth is available close to the current price, and volatility remains manageable.
Under these conditions, liquidity providers can quote narrow spreads because they expect to offset positions relatively easily.
The Bank for International Settlements explains that market makers tend to quote narrower spreads when assets can be traded, funded, and hedged quickly and cheaply. Their inventory risk is easier to manage when related markets are liquid and stable.
Imagine a heavily traded large-cap stock during normal market hours.
Thousands of shares may continuously appear at both the bid and ask. If one market maker quotes too wide a spread, competing firms can offer better prices and capture the order flow.
Competition pushes transaction costs downward.
CME’s liquidity framework therefore evaluates spreads alongside book depth and cost-to-trade statistics rather than treating the spread as an isolated number.
A consistently narrow spread usually indicates healthy competition for trading activity.
Volatility Can Push the Market Into a Wider-Spread Regime
The situation changes quickly when volatility rises.
Imagine a market maker offers to buy at $100.00 and sell at $100.02.
If the asset moves only a few cents every minute, maintaining those quotes may be relatively safe.
Now imagine price begins moving $1 every few seconds.
The market maker could buy at $100 only to watch the market immediately fall toward $98.50.
To compensate for that increased risk, liquidity providers can reduce order sizes, cancel quotes, or widen their bid-ask spreads.
CME research notes an inverse relationship between volatility and liquidity, observing that periods of elevated volatility can coincide with reduced order-book depth and wider effective spreads.
The BIS describes a similar feedback mechanism. Rising volatility increases inventory risk for market makers, which can encourage them to reduce risk-taking. If many liquidity providers do this simultaneously, spreads may widen and liquidity can deteriorate further.
This is why spreads sometimes expand dramatically during news events even when trading volume is enormous.
High volume does not automatically mean low execution costs.
Market Depth Changes the Meaning of a Tight Spread
A tight spread can look reassuring while hiding a shallow order book.
Suppose Bitcoin has:
Bid: $99,995
Ask: $100,005
The spread is only $10, or roughly one basis point.
That looks extremely liquid.
But imagine only $20,000 worth of BTC is available at the best ask and relatively little additional liquidity exists above it.
A $2 million market buy would quickly consume that quote and move through higher price levels.
CME defines central limit order book liquidity using both spread and depth, including the quantity available at the best price.
So traders should never read the spread alone.
A strong liquidity regime generally combines narrow spreads with meaningful depth and manageable price impact.
A fragile regime can still display a narrow top-of-book spread while liquidity underneath is disappearing.
This becomes particularly relevant during a sudden volatility spike, when displayed depth can fall much faster than the headline spread initially suggests.
Stress Regimes Can Produce Wider Spreads but Heavy Trading
One counterintuitive point is that stressed markets can have wider spreads while simultaneously producing record trading volume.
That is not a contradiction.
During April 2025’s period of elevated U.S. equity volatility, CME reported that E-mini S&P 500 futures volume on April 7 was more than 99% above the Q1 average daily volume even though order-book depth had fallen about 68% relative to the previous week.
The market was extremely active but less comfortable to trade.
This demonstrates why volume alone is an incomplete liquidity metric.
Liquidity providers may continue replenishing orders after existing quotes are consumed, allowing large amounts of volume to execute despite shallow displayed depth.
CME argues that spread, book depth, execution quality, fill rates, and price impact should therefore be considered together.
For traders, the lesson is practical.
Do not assume that a busy market is necessarily a cheap market to trade.
During a stressed regime, huge volume can coexist with worse execution.
Quoted Spread and Effective Spread Are Not the Same
The spread displayed on your screen is the quoted spread.
The actual trading cost can be different.
The SEC describes effective spread as a measure based on the difference between the actual execution price and the bid-ask midpoint when the order arrived.
This distinction matters because trades can execute inside the quoted spread.
Alternatively, larger orders may walk through multiple levels and experience costs far beyond the best displayed ask or bid.
Imagine a market quoted:
$100.00 bid / $100.10 ask
The quoted spread is $0.10.
If your buy executes at $100.05, your effective cost relative to the midpoint may be lower than simply paying the displayed ask.
But if a large order fills partly at $100.10, $100.20, and $100.35, the top-of-book spread dramatically understates the real execution cost.
Kaiko similarly notes that effective spreads can provide a better picture during stressed conditions because they incorporate actual executed prices and available liquidity.
For large trades, slippage and price impact therefore matter just as much as quoted spread.
Crypto Spreads Depend Heavily on Venue and Trading Pair
Stocks and crypto share many microstructure principles, but crypto introduces much greater venue fragmentation.
Bitcoin may simultaneously trade against USD, USDT, EUR, and other currencies across numerous exchanges.
Each market can have a different spread.
Kaiko has documented significant differences between cryptocurrency venues and quote assets, with more liquid pairs generally showing tighter spreads. It also notes that spreads typically widen as volatility increases because market makers face greater risk from rapid price changes.
Liquidity is also concentrated.
Kaiko found that a relatively small group of exchanges accounts for most global crypto market depth, meaning the liqudity available on one venue may differ dramatically from the broader market.
Consider an altcoin trading with a 10-basis-point spread on Exchange A but a 60-basis-point spread on Exchange B.
The asset has not fundamentally changed between platforms.
The market-making competition, depth, inventory risk, order flow, and available hedging opportunities have.
This is why crypto traders should compare venues rather than assuming one exchange represents the global market.
Different Assets Naturally Operate in Different Spread Regimes
Not every wide spread indicates temporary market stress.
Some assets are structurally less liquid.
A mega-cap stock trading millions of shares each day may regularly operate near the minimum permitted price increment.
A thinly traded small-cap stock might naturally carry a much larger spread.
The same pattern appears in crypto.
Bitcoin and Ethereum typically have stronger liquidity infrastructure than many smaller tokens.
Kaiko research has found that altcoins can experience greater deterioration in depth during market stress because they often have thinner books, fewer liquidity providers, and less institutional participation.
This creates different baseline regimes.
A five-basis-point spread might look terrible for a highly liquid BTC pair but excellent for a thinly traded altcoin.
The useful question is therefore not:
“Is this spread wide?”
Ask:
“Is this spread unusually wide relative to this asset, venue, time of day, and volatility environment?”
Historical distributions can make that distinction much clearer.
Time of Day Can Change the Spread Without Changing the Asset
Liquidity has an intraday rhythm.
Stock markets often experience extremely active periods around the open and close, while trading conditions can differ significantly during quieter periods.
Global derivatives and crypto markets also experience shifting liquidity as Asian, European, and U.S. trading sessions overlap.
CME’s liquidity tools specifically allow spreads and depth to be compared across Chicago, London, and Singapore trading windows.
Crypto trades 24/7, but its liquidity does not remain constant 24/7.
Market-maker participation, institutional activity, macroeconomic releases, and weekend trading can all change conditions.
A spread that appears normal during a quiet Sunday may be abnormally wide during peak weekday activity.
The same principle applies around major announcements.
If the spread expands dramatically just before an inflation report or central-bank decision, liquidity providers may simply be reducing risk until uncertainty clears.
That does not necessarily signal a long-term deterioration in the market.
Use Spread Regimes as a Trading-Risk Indicator
Spread analysis becomes much more useful when traders monitor how the spread is changing rather than just reading its current value.
Imagine a stock normally trades with a two-cent spread.
Over several minutes, it widens to four cents, then eight cents, while book depth falls and volatility rises.
Something in the market’s risk profile is changing.
That spread expansion can serve as an early warning that execution is becoming more difficult.
Conversely, after a volatility event, spreads gradually tightening while depth returns can indicate liquidity providers are becoming more comfortable again.
Kaiko observed this type of recovery following stressed crypto-market conditions, where restoring market depth and declining spread volatility indicated stronger liquidity-provider confidence.
A practical dashboard might therefore monitor quoted spread, effective spread, depth, slippage, volatility, and volume together.
The objective is not to predict price direction from the spread.
It is to identify the liquidity regime in which you are trading.
That can influence order type, position size, execution strategy, and how much slippage you should realistically expect.
Bid-ask spreads are more than a small number between two prices. They provide a real-time clue about competition, liquidity, volatility, inventory risk, and the cost of demanding immediate execution.
In calm and deep markets, competition among liquidity providers generally keeps spreads tight. When volatility rises, market makers may reduce risk, depth can disappear, and spreads expand.
Yet even stressed markets can process enormous trading volume, which is why spread analysis should always include depth, effective execution costs, and price impact.
Most importantly, evaluate spreads relative to the asset’s normal environment. Compare them across time, venues, and volatility regimes instead of relying on one snapshot.
Tracking those changes can help you recognize when trading conditions have shifted before the higher execution costs become an unpleasant occurence.
