Volume, open interest and participation

Chapter 1 named three inputs. Two of them — price and volume — have appeared throughout. This chapter is the third, and it deserves its own treatment because it is structurally unlike the others.

Volume, restated

From chapter 2: volume is matched quantity. Every transaction has a buyer and a seller, so the quantity bought equals the quantity sold, always.

What volume indicates is how much actually traded — participation in the literal sense. A price move on heavy volume involved more of the instrument changing hands than the same move on light volume. That is a factual difference and worth knowing.

What it does not indicate is direction of pressure, for the reason above.

Open interest, which is different

Open interest is the number of contracts currently outstanding — positions opened and not yet closed. It exists only for derivatives, because only a derivative creates a contract that can remain open.

The mechanics are precise. Every futures trade pairs a buyer with a seller, and each of them is either opening a new position or closing an existing one. That gives four combinations:

Buyer	Seller	Effect on open interest
Opens (new long)	Opens (new short)	+1 — a new contract exists
Opens (new long)	Closes (was long)	0 — the position transferred
Closes (was short)	Opens (new short)	0 — transferred the other way
Closes (was short)	Closes (was long)	−1 — a contract is extinguished

So volume and open interest answer different questions. Volume asks how much changed hands. Open interest asks how much remains committed.

A day can have enormous volume and no change in open interest at all — that is a day of position transfer, with as many people leaving as arriving.

Why this is the interesting input

Here is the thing that makes open interest worth a chapter: it is not a function of price.

Every indicator in chapters 3 to 6 is computed from the closing price series. Chapter 6 made the point sharply — RSI and MACD contain no information the closes did not hold, which is why their agreement is not corroboration.

Open interest is independent data. You cannot derive it from the price series; it comes from the clearing corporation's record of outstanding positions. It is a genuinely separate observation about the market.

That makes it the one input in this subject that could in principle add something — and it is correspondingly less discussed than the indicators that cannot.

Its honest limits are the same as everything else here, though. It tells you how many contracts are open, not who holds them, why, or whether those positions are hedges against a real exposure or speculation. The Derivatives subject's distinction between hedging and speculating is invisible in the number — a farmer hedging a crop and a trader betting on direction both add one to open interest.

Participation, and what it has meant in India

SEBI publishes participation data for the equity derivatives segment, and it gives this chapter's abstractions a concrete setting.

As the Behavioural finance subject set out, the number of individual traders rose toward 96 lakh in FY25 while 91% of them lost money, a share stable between 90% and 92% across four years.

Two things follow that are relevant here.

Rising participation is not a bullish indicator or a bearish one. It is a count of people in the market. In this case the count rose and the outcomes did not improve, which is a caution against reading participation as validation.

Open interest growth in a retail-heavy market tells you about the composition of the market, not about where the price is going. More open positions held by a population that loses money 91% of the time is a different fact from more open positions held by hedgers, and the number alone does not distinguish them.

Working the problem

Volume 10,000, open interest up 2,000.

What must have happened. Use the table. Of the 10,000 contracts traded:

• 2,000 were new-long-meets-new-short, each creating a contract. Open interest +2,000.
• The remaining 8,000 were some mixture of transfers (one side opening, one closing — no effect) and mutual closes (both closing — which would reduce open interest).

So strictly: (new pairs) − (mutual closes) = 2,000, with the balance of the 10,000 made up of transfers. If there were, say, 500 mutual closes, then there were 2,500 new pairs and 7,000 transfers.

What you can conclude: net new commitment entered the contract. More positions are open at the end of the day than at the start, so on balance participants added exposure rather than unwinding it.

What you cannot conclude — and this is the longer list:

Direction. New longs and new shorts were created in equal number, because they must be. The 2,000 new contracts are 2,000 new long positions and 2,000 new short positions. Open interest rising is not bullish. It is widely reported as though it were, and the arithmetic forbids it.

Who. Hedgers, speculators, arbitrageurs, or a market maker warehousing inventory — all the same in the number.

Conviction. A position opened on a whim and one opened after months of analysis each add one.

What happens next. The number describes commitments now, not outcomes later.

The honest summary: rising open interest with rising price is often described as confirming a trend. What it actually establishes is that new positions were opened on both sides while price rose. Whether that means anything is the question chapter 9 takes up — and the answer there applies to this as much as to any moving average.

The point

Volume counts matched quantity, so it cannot show net buying; open interest counts contracts outstanding, and each trade either creates, transfers or extinguishes one depending on whether each side is opening or closing. A day of heavy volume with unchanged open interest is pure position transfer. Open interest matters because, unlike every price-derived indicator in this subject, it is independent data from the clearing record — the one input that could add something. But it names no direction, since every new contract creates a long and a short together, and it says nothing about who holds the position or why.