Open Interest Explained: The Core of OI Analysis

Defining Open Interest

Open interest (OI) is the total number of outstanding option contracts for a strike and expiry that remain open — not yet squared off or settled. If trader A sells a call to trader B, OI increases by one lot. If B later sells to C, OI stays the same — the contract changed hands but was not closed.

OI is slow-moving compared to price. That is precisely why it is valuable. Price tells you what happened; OI hints at who is positioned and whether new risk entered the market.

Interpreting OI Change with Price

The classic OI analysis matrix pairs price direction with OI change. New positions increase OI; closing positions decrease it. Combining this with call vs put side tells a richer story than price alone.

On index options, sudden OI spikes at a single strike often precede intraday battles — writers defending levels, or aggressive buyers building directional bets. Watch OI spurts screens to catch these early.

• Long buildup: price and OI both rising — conviction longs entering
• Short buildup: price falling, OI rising — aggressive shorts or put writing
• Short covering: price rising, OI falling — bears exiting, rally fuel
• Long unwinding: price falling, OI falling — bulls giving up

Strike-Level vs Index-Level OI

Strike-level OI shows battlefield lines on the option chain. Index-level aggregated OI and PCR summarise sentiment. Both views matter. A single strike may show massive call writing while overall PCR looks neutral — the detail hides in the chain.

Multi-strike OI charts reveal how OI migrates through the session. When OI shifts from lower strikes to higher strikes on calls, it can signal bullish repositioning as spot trends up.

Common OI Mistakes

Treating OI as a directional oracle is the biggest mistake. OI shows positioning, not intent with certainty. Writers may hedge elsewhere; rolling from one expiry to another distorts daily change figures.

Second mistake: ignoring volume. OI without volume can be stale — old positions sitting idle. Third: overfitting one strike on expiry day when gamma effects dominate. Combine OI with Greeks awareness as expiry nears.