# Open interest versus volume

**FUT-16 · Equity Index Futures · Core**

**Lesson question:** What changes when a contract changes hands?

Original fictional examples; educational writing, not live market data, orders or production approval.

## By the end

- Explain the mechanism in the lesson question.
- Reproduce the worked comparison and recognize its failure case.

**Prerequisites:** FUT-01

Open interest counts outstanding contracts after positions are netted. Volume counts completed trades during a period. A contract can trade many times without creating a new outstanding contract on every transaction.

Keeping these measures separate prevents overstating new positioning.

## Understand the mechanism

If both parties open, OI rises by one. If both close, it falls by one. If one opens while the other closes, the position changes hands without necessarily changing OI. Every transaction adds volume.

OI also has a reporting time and does not identify a universal dealer direction: every contract has a long and a short.

## Walk through the process

Compare matching periods and contract months. During a roll, OI can decline in one month and rise in another without a comparable change in aggregate exposure.

Describe what the data support instead of treating a higher unsigned count as inherently bullish or bearish.

## Operational boundary

All figures are fictional teaching inputs, not current quotes or margin schedules. Product rules, broker requirements and usable liquidity remain separate from the model example. A planned exit and an algebraic hedge are not execution guarantees.

## A worked example

Start with fictional OI 1,000. One hundred new/new trades raise it to 1,100. Fifty close/close trades reduce it to 1,050. Two hundred opening/closing transfers leave it at 1,050.

Volume across the sequence is 350 while OI changes only +50. The graph tracks outstanding contracts after each stage.

## Graph: Open interest versus volume—worked comparison

**Horizontal:** Opening/closing/transfer stage  
**Vertical:** Open interest (contracts)

Fictional data from the written example. The chart organizes the comparison; its shape is not a forecast.

Complete numerical data are embedded in `scripts/equity-futures/FUT-16.js` and displayed as an accessible table in the HTML lesson.

## What would invalidate the reading?

Counting all volume as new OI overstates position creation. Inferring dealer sign from the total is a second unsupported step.

## Check your understanding

### What are final OI and volume?

**Answer:** OI 1,050; volume 350.

**Why:** Creation and destruction affect OI, while every trade contributes volume.

### What is the critical failure to avoid?

**Answer:** Counting all volume as new OI overstates position creation. Inferring dealer sign from the total is a second unsupported step.

**Why:** Explain this risk before treating the example as a decision rule. A correct calculation does not guarantee a favorable market outcome. **Critical risk check.**

## Takeaway

Return to the question: What changes when a contract changes hands? State the observed facts, the assumptions and the failure condition separately.

## References and provenance

The cited references support definitions and conventions. The teaching prose, tickets and numerical scenarios are original; they are not attributed as historical market observations.

- [CME Introduction to Futures](https://www.cmegroup.com/education/courses/introduction-to-futures)

- [CME Micro E-mini overview](https://www.cmegroup.com/education/courses/micro-e-mini-futures/micro-e-mini-futures-products-overview)