If you have looked at the option chain, you will always see a column called OI. Traders often hear things like “OI is rising” or “there is short buildup” or “this strike has high OI”, but it is not always clear what all of this really means or how to use it.
Let’s break it down in the simplest way possible.
What is OI
OI stands for Open Interest. It shows how many option contracts are currently open in the market.
If OI is 1,00,000 at a strike, it simply means there are 1,00,000 open positions at that level. That’s it.
OI does not tell you whether these positions are buys or sells. It only tells you that positions exist.
How OI moves
OI changes when traders enter or exit positions.
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OI rising means more positions are being created.
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OI falling means positions are being closed.
This is the only thing OI tells you. The interpretation comes from combining OI with price.
How to read OI with the underlying price
This is where it becomes useful.
1. Underlying Price up and OI up
This means new long positions can be entering. Traders are building confidence on the upside.
2. Underlying Price down and OI up
This usually means new short positions are being added. Traders are betting on more downside.
3. Underlying Price up and OI down
This indicates longs are closing. People are booking profits or cutting exposure.
4. Underlying Price down and OI down
This indicates shorts are closing. Traders are covering their positions.
These are not guaranteed outcomes but simple, practical ways traders look at OI.
OI as support and resistance
When a strike has very high OI, it often behaves like a wall.
For example:
If the 25000 CE has very high OI, it means a lot of traders have positions there. These traders do not want the market to cross that level easily. That strike may act as resistance.
Similarly, if 24800 PE has high OI, it may act as support.
But remember, markets do break these levels when momentum is strong.
How to actually use OI
Here is the simple way:
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Check where the highest Call OI is. This is your potential resistance zone.
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Check where the highest Put OI is. This is your potential support zone.
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Look at how OI is changing during the day. Rising OI shows participation.
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Do not rely on OI alone. Combine it with price movement and volume.
A quick example
Say NIFTY is at 24850.
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25000 CE shows huge OI.
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24800 PE shows huge OI.
This tells you the market may stay in this range unless one side starts unwinding.
If suddenly 25000 CE OI starts decreasing while price moves up, it means resistance is weakening.
Bottom line
OI tells you how many traders are active at a strike.
Price tells you who is winning.
Combine both and you get a clearer picture of whether the market is building long positions, short positions, or closing them.
Once you start reading OI with price, support and resistance will make much more sense and your option chain reading becomes more meaningful.