Why Liquidity Can Vanish Just When Markets Need It Most

Two Kinds of "Liquid" — and Why the Difference Matters

Picture a busy vegetable mandi on a Sunday morning. You can sell your tomatoes instantly, at a price everyone roughly agrees on. Now picture the same mandi at 3 a.m. on a Tuesday: almost no buyers, prices anyone's guess. The tomatoes haven't changed. What changed is the market around them.

That is market liquidity — the ability to rapidly execute sizeable transactions at low cost and with limited price impact, as the European Central Bank describes it. It is not one thing but several: immediacy (how fast a trade settles), breadth and depth (how much can trade without moving the price), and tightness (the gap between buying and selling prices).

Now the second kind: funding liquidity. This is the ease with which financial firms can borrow — to hold positions, to post collateral, to keep the lights on. The ECB breaks funding risk into three flavours: rollover risk (short-term borrowing can't be renewed), redemption risk (depositors or investors pull money out), and haircut/margining risk (collateral is suddenly valued less, or margins rise).

The two are connected, and that connection is where the trouble lives.

The Plumbing Between Them

Consider a dealer who "makes a market" in bonds — quoting a buying and selling price all day. To do this, the dealer must be willing to hold bonds on their own balance sheet when clients want to sell. That takes financing. Typically, the dealer borrows in the repo market, pledging those very bonds as collateral. Market liquidity, in other words, runs on funding liquidity.

Now suppose funding gets harder. Margins rise. Haircuts increase (a haircut is the discount lenders apply to collateral — if a bond worth ₹100 is accepted at ₹95, the haircut is 5%). The dealer's capacity to hold positions shrinks, so they quote wider spreads or stop quoting entirely. Market liquidity thins. Prices swing more wildly. And here's the twist: higher volatility can trigger further margin increases. As the ECB puts it, the two dimensions "can reinforce each other in ways that generate liquidity spirals." Under extreme conditions, markets can stop functioning altogether.

The research of Brunnermeier and Pedersen, whose work underpins much of this thinking, frames it neatly: traders need funding to provide market liquidity, and their funding depends on market liquidity through collateral values. The snake eats its tail.

Margin Calls: The Accelerator

Margin requirements are calculated using risk models — and those models behave procyclically. A Bank of England financial stability paper explains it plainly: margin requirements for the same portfolio are higher during market stress and lower in calm times. This makes sense from a risk-management view (volatility is genuinely higher), but it means firms must find extra liquid assets at precisely the moment those assets are hardest to find.

Real episodes bear this out. The Financial Stability Board points to the Archegos Capital collapse in 2021 and the United Kingdom's liability-driven investment stress in September 2022 as examples where rapid increases in margin and collateral requirements "amplify liquidity needs across the financial system, especially if market participants are unprepared."

The FSB's December 2024 guidance for non-bank firms — hedge funds, pension funds, insurers, family offices and commodity traders — recommends stress-testing for exactly this: both historical and hypothetical scenarios, with attention to concentrated and leveraged exposures, and to the market impact of asset liquidations under stress.

Prime Brokerage: Leverage With a Timing Problem

Prime brokerage is the bundle of services — leverage via margin loans and securities financing, custody, clearing, market access — that broker-dealers, often inside large banking groups, provide to hedge funds. The Bank for International Settlements notes that hedge funds rely on just a few prime brokers, with the largest each serving more than 1,000 funds.

This concentration creates two-way risk. The BIS highlights wrong-way risk: the chance that a broker's exposure to a fund grows exactly when the fund's likelihood of default rises. Opaqueness makes it worse — a broker may not see the fund's positions at other banks. In the Archegos episode, prime brokers were not fully aware of the size of the fund's positions elsewhere, underestimating its overall leverage. One affected broker had also not set sufficiently conservative leverage terms.

There's a cyclical pattern too. The BIS finds that secured borrowing by hedge funds correlates with stock market valuations — leverage is procyclical. Prime brokers accommodate requests for better margin terms during calm periods, then tighten when volatility arrives. It's a bit like a gym that offers generous membership terms in January and reconsiders in March. Except with systemic consequences.

Stablecoins: A Newer Channel

Stablecoins — digital tokens designed to hold a steady value, usually pegged to the dollar — add a modern wrinkle. A 2025 Federal Reserve note explores how stablecoin growth could reshape bank deposits and funding. The key point for our purposes: how stablecoin issuers hold their reserves matters enormously.

If issuers keep reserves mostly as bank deposits, aggregate deposit volumes may hold up, but their composition shifts — from insured retail deposits to uninsured wholesale ones. Those wholesale balances "might move rapidly in response to market signals or redemption activity," the Fed note observes. The Silicon Valley Bank failure in 2023 showed how quickly uninsured deposits can flee when confidence wavers.

Formal stablecoin redemptions typically take longer than ordinary deposit withdrawals, so the Fed cautions that any liquidity advantage is situational rather than universal. The note also flags concentration: a limited number of banks serve the issuers, so correlated redemptions across multiple stablecoins could create simultaneous pressure on the same institutions.

Why This Is Hard to Measure

One uncomfortable truth: market liquidity isn't directly observable. The ECB notes that tight bid-ask spreads — often read as a sign of abundance — may conceal that very little volume is actually available at those quotes. Data on corporate bond liquidity is sparse because trading remains fragmented and largely over-the-counter.

Regulatory ratios like the Liquidity Coverage Ratio are static, on-balance-sheet measures. A paper modelling German banks' behaviour argues such ratios "might reflect a too optimistic view" because they don't capture strategic interactions — how banks' collective rush to sell assets depresses prices for everyone. In a simulated five-day system-wide run, that paper estimated a market-value loss of about €55 billion across German banks, roughly 8% of aggregate Tier 1 capital.

What Actually Helps

The ECB's analysis suggests a funding shock tends to disrupt market liquidity significantly, while the reverse is more limited — particularly when central bank reserves are low or declining. Reserves act as a buffer: when cash is plentiful, banks can meet obligations without selling assets into stressed markets.

That's the practical lesson for anyone watching markets. Liquidity is a fair-weather friend. It looks abundant until the moment you need it, which is why regulators emphasise diversified collateral, tested contingency plans, and stress scenarios that assume the worst timing. The FSB also stresses regular counterparty engagement — agreements reviewed and tested before the storm, not during it.

None of this predicts any particular outcome, and rules differ meaningfully by jurisdiction and entity type. But understanding the plumbing — that funding and market liquidity are linked, that margins amplify, that leverage concentrates — makes the headlines easier to read and the risks easier to respect. And it's a useful reminder that in finance, as in a mandi, the price on the board only means something if someone will actually trade at it.