Open Interest (OI)

Volume tells you how many contracts changed hands today; open interest (OI) tells you how many are still *live*. It is the total number of outstanding futures or options contracts that have been opened but not yet closed, exercised or expired — a running tally of the market's commitment to a position, and one of the most powerful tools in F&O analysis.

How OI Moves

OI rises when a new buyer and a new seller create a fresh contract, and falls when existing holders close out. This is different from volume: two traders simply passing an existing contract between them generates volume but no change in OI. Reading OI alongside price gives clues about the strength behind a move:

- Price up + OI up → new long positions, strong bullish trend. - Price down + OI up → new short positions, strong bearish trend. - Price up + OI down → short covering, a weaker rally. - Price down + OI down → long unwinding, a weaker decline.

OI in the Indian F&O Market

Indian traders watch OI obsessively on Nifty, Bank Nifty and stock options. The distribution of OI across strike prices reveals where the market expects support and resistance — heavy call OI at a strike often marks a resistance ceiling (writers betting price won't cross it), while heavy put OI marks a support floor. The max pain concept and the Put-Call Ratio (PCR), both derived from OI, are widely used to gauge sentiment. SEBI and the exchanges also impose OI-based market-wide position limits to prevent excessive concentration.

Why It Matters

OI is essentially a measure of liquidity and conviction. High OI means a contract is liquid and the trend has real money behind it; thinning OI warns that participants are exiting and a move may fizzle. For options buyers and writers alike, tracking changes in OI at key strikes is central to anticipating where the index might find support or face resistance into expiry. It turns the raw price chart into a richer story about who is positioned, and how strongly.