Basic Points

• Options Open Interest (OI) is the total number of options contracts that have been opened and not yet closed. 
• In other words, OI is the total number of options that are currently open for calls or puts.
• When we speak generally of OI, the meaning is the sum of both call and put OI.
•  However, for extra detail, we post the “put OI” and “call OI” each day to our members. This extra amount of detail (comparing put to call OI) can be useful, for example to see if either part of the spectrum is dominating. 

<Additional Key Levels Table from the SpotGamma Founder's Note>

As the primary restriction of OI, the actual positioning of OI (dealer vs aggressor) is not available until 2 weeks later. Also, unlike volume, which changes throughout the day, OI only gets updated each day after the close. 

When a new option contract is bought, it increases the open interest, and when an existing contract is closed or exercised, it decreases the open interest. Open interest can be used to gauge the level of activity in the options market and to get a sense of the sentiment of market participants. For example, a rising open interest may indicate that new money is coming into the market and that traders are bullish on the underlying asset if that OI is getting poured into calls. 

On the other hand, a falling open interest (from calls) may indicate that traders are becoming less optimistic. Open interest is typically reported on a daily basis and can be found in financial news sources and market data providers, however we provide the additional service of parsing put from call OI for you to have access to that extra detail.