Overnight Index Swap

What Is an Overnight Index Swap?

An Overnight Index Swap (OIS) is an interest rate swap in which one counterparty pays a fixed rate while receiving — or vice versa — the compounded daily overnight reference rate (such as SOFR in the US, €STR in the Eurozone, or SONIA in the UK) over the agreed tenor. Because the floating leg resets each business day and the notional principal never changes hands, counterparty credit risk is minimal, making OIS rates a clean proxy for risk-free rate expectations over a given horizon.

The OIS fixed rate encodes the market's probability-weighted path for the central bank's policy rate. A 1-year OIS rate of 4.75%, for example, implies the market expects the average overnight rate to be roughly 4.75% over the next twelve months. Traders and economists use OIS curves to back out the number and magnitude of rate hikes or cuts priced into the market at any point in time.

Why It Matters for Traders

OIS rates are the foundation of modern derivatives pricing. When banks replaced LIBOR with risk-free rates during the IBOR Transition, OIS became the standard discount rate for most collateralized derivatives. This means moves in the OIS curve directly affect the present value of every swap, structured product, and futures contract that is collateralized under a Credit Support Annex (CSA).

For macro traders, the LIBOR-OIS spread — now more commonly the term SOFR vs. OIS spread — is a real-time gauge of interbank funding stress. When OIS rates diverge sharply from Treasury bill yields, it signals that market participants are pricing elevated credit risk or liquidity hoarding in the banking system. OIS-to-Fed-Funds comparisons also reveal whether the Fed is executing policy as intended.

How to Read and Interpret It

• OIS curve slope: A steeply upward-sloping OIS curve implies the market expects rate hikes; an inverted OIS curve prices rate cuts. The 2s10s OIS spread is watched alongside the traditional Treasury yield curve.
• OIS vs. Fed Funds effective rate: A persistent spread >5 bps may signal implementation friction in the Fed's operating framework.
• LIBOR-OIS (historical) or term rate-OIS spread: Spreads above 30–40 bps have historically coincided with acute funding stress (e.g., the 2008 crisis saw LIBOR-OIS exceed 350 bps).
• Meeting-to-meeting OIS pricing: Central bank watchers parse 30-day OIS contracts expiring around each FOMC meeting to extract implied probabilities for 25 bps vs. 50 bps moves.

Historical Context

The OIS market gained global attention during the Global Financial Crisis of 2008. The 3-month USD LIBOR-OIS spread, which had traded below 10 bps for years, exploded to approximately 364 basis points in October 2008 as Lehman Brothers collapsed. This spread became the single most-watched metric of systemic banking stress for policymakers at the Federal Reserve and Treasury. The Fed's emergency liquidity facilities were explicitly designed to compress it. By mid-2009, the spread had returned to roughly 25 bps, signaling stabilization.

More recently, during the March 2020 COVID shock, the 3-month LIBOR-OIS spread widened to approximately 138 bps before the Fed's dollar swap lines and repo operations drove it back below 20 bps within weeks.

Limitations and Caveats

OIS rates reflect market-implied expectations, not guaranteed outcomes. Survey-based forecasts and OIS pricing frequently diverge, especially during periods of high uncertainty. Additionally, the liquidity of OIS contracts varies by tenor and currency — the very short end is highly liquid in USD, but longer-dated OIS in emerging market currencies can be thin and prone to distortion. Cross-currency differences in conventions (compounded vs. simple averaging) also complicate direct comparisons.

What to Watch

• The SOFR OIS curve at each FOMC-dated maturity for live rate-cut or hike pricing.
• Cross-currency OIS differentials (e.g., USD vs. EUR OIS) as drivers of cross-currency basis swap dynamics.
• OIS spreads to T-bills around quarter-end for signs of window dressing or reserve scarcity.
• The Fed's reverse repo facility usage relative to OIS to monitor the ample reserves regime.