2008 Money Market Fund Run

When the Reserve Primary Fund broke the buck in September 2008, it shattered the assumption that money market funds were as safe as cash. Within weeks, the $3 trillion money market sector faced a run that threatened to freeze short-term credit markets across the entire US economy.

Why money market funds were thought to be safe

Money market funds occupy a peculiar niche in the financial system. They are not insured like bank deposits, yet they promise net asset value stability at $1 per share. They hold short-term debt: commercial paper from corporations, treasury bills, and repurchase agreements. For decades, the threat of a fund “breaking the buck”—falling below $1 per share—seemed academic. The Reserve Primary Fund, the largest such fund in America, had never broken the buck in its 14-year history. Investors treated money market fund shares as a cash alternative, with yields slightly higher than bank accounts and only marginally more risk. Institutional treasurers, mutual funds, and corporate cash managers held billions there.

The illusion rested on two unstated assumptions: issuers of commercial paper would not default, and markets for these instruments would always have a bid. Neither assumption survived September 2008.

The trigger: Lehman Brothers and credit panic

On 15 September 2008, Lehman Brothers, a primary market dealer and major issuer of commercial paper, collapsed. The Reserve Primary Fund held nearly $800 million in Lehman debt. Overnight, the value of that holding became uncertain. As news spread, the fund faced a problem: if it marked the Lehman holdings to fair value, the fund’s $62 billion in assets would drop below $62 billion in liabilities, breaking the buck. The fund’s managers faced an immediate choice: use conservative accounting or hope the Lehman debt recovered. They hesitated. On 16 September, the Reserve announced a loss on the Lehman holdings, and the fund’s per-share value fell to $0.97. That was the break of the buck.

The impact was instant and visceral. Investors who had assumed money market funds were “as safe as cash” discovered they were not. Redemptions started. Within days, withdrawals accelerated. Redemption requests overwhelmed inflows. The fund, unable to meet all demands immediately, imposed restrictions on withdrawals—something money market funds simply do not do. For investors, this was a sign of systemic stress.

The contagion spreads

The Reserve Primary Fund’s crisis was not isolated. Other large funds held Lehman paper or similar at-risk commercial paper. Credit markets began to seize. Issuers of new commercial paper found few buyers. Corporations, dependent on rolling over short-term funding, faced a funding cliff. Major money market funds, facing massive redemption requests, had to sell assets into an illiquid market at fire-sale prices, crystallizing losses. Several funds gated redemptions. The liquidity crisis fed on itself: fear drove withdrawals, withdrawals forced fire sales, fire sales drove losses, and losses drove more withdrawals.

Prime money market funds—those holding commercial paper and corporate bonds—saw outflows of roughly $200 billion over two weeks. Funds trying to preserve stability had to park cash in the least risky instruments: Treasury bills. But Treasury yields had collapsed to near zero, and all funds were doing the same thing simultaneously, creating a stampede.

Government intervention

The Federal Reserve and Treasury recognized the threat. Money market funds were not just retail investments; they were a critical channel through which US corporations accessed short-term credit. If that channel froze, non-financial companies would lack working capital, and the recession would deepen sharply. A system collapse was plausible.

The Fed implemented several measures. The Federal Reserve established a Commercial Paper Funding Facility (CPFF) to buy newly issued commercial paper directly, bypassing the money market fund sector entirely. This provided alternative funding sources for issuers. The Securities and Exchange Commission (SEC) permitted money market funds to impose redemption fees and, in extreme cases, to gate redemptions—removing the assumption that shares were instantly redeemable at $1.

Most crucially, the Treasury launched the Temporary Guarantee Program for Money Market Funds, guaranteeing the principal value of shares in enrolled funds as of 21 September 2008. This guarantee meant that even if a fund broke the buck, investors would be made whole up to $1 per share. The message was clear: the Treasury stood behind money market funds. Investor confidence, which had evaporated, gradually returned.

Why this happened: structural vulnerabilities

The crisis exposed a fundamental mismatch in money market fund structure. Funds held illiquid assets—commercial paper with maturities extending weeks or months—yet promised daily redemption rights. They also pursued stable net asset value at $1, even as their portfolios fluctuated in value. In normal times, new money flowing in covered redemptions, and yields were positive. But when credit markets cracked, the structure became untenable. Funds could not simultaneously honour the redemption promise, mark assets fairly, and maintain a $1 share price.

The reliance on short-term commercial paper made funds vulnerable to any spike in credit risk or liquidity concerns. A Lehman collapse, a major default, or even a rumour of default could spark redemptions. And once redemptions began, funds faced a dilemma: meet them by fire-selling assets (crystallizing losses) or gate redemptions (breaking the implicit promise of daily liquidity). Investors, having assumed safety, responded to either outcome with panic.

Post-crisis reforms

The SEC tightened money market fund rules substantially. Prime money market funds (those holding commercial paper) faced new liquidity requirements, forcing them to hold a higher share of instruments redeemable within days. Expense ratios were capped to prevent fee compression during stress. Fund managers were no longer permitted to amortize losses or use subjective valuation to hide deteriorating net asset value. Certain funds were required to use mark-to-market accounting, showing true value daily. Floating net asset value was introduced for institutional prime and tax-exempt funds, ending the fiction of a stable $1 share price.

These changes reduced the appealing arbitrage that had sustained the sector: high yields without perceived risk. As a result, money market fund assets shrank, and some investors shifted to other short-term instruments. But the systemic risk of a cascading liquidity crisis diminished substantially.

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