Correlation between ES Expiration Date, OI and Mkt trend change

zippo

Hope HT friends can help answer my question:

At the end of each quarter when ES expire, the OI dropped drematcilly.  Why this happens?  If ES can be rolled over to the next Qtr, would OI should not change much?  Maybe I am on the wrong path?  The reason I am asking, it seems the SPX reverses trend near the end of Qtr when ES expires and OI dropped.  Attached is a ES Wkly chart.

benmao

when es contract expired, it will be cash settlement, rollout will need manual handling.

during sept 2009 when es was about to expire, traders might close esu9 positon and open esz9 position.

zippo

2# benmao

I thought the OI in the above chart is total contract.  does not matter which Qtr. of ES future? Maybe I am wrong.