In order to reduce volatility in various scrips at the start of the market and arrive at the ideal opening price of the scrip, the exchanges are introducing call auction process in Pre open session from 18th October 2010. Therefore under this new arrangement, the exchange will collect the orders for the first few minutes of this session. On the basis of orders received, the exchange will arrive at Opening Price and match the tradable orders on that price. Remaining orders will be moved to normal trading session. The call auction process will be initially introduced for scrips forming part of Nifty and Sensex and trading in Non Nifty / Sensex scrips and F&O contracts will only begin at 9:15 A.M when normal market trading begins. Please note that orders not will get traded during the time when order entry period is on in the Pre open session. The duration of Pre-Opening Session will be of 15 minutes – from 9:00 A.M. to 9:15 A.M. The session will have three phases -
| Session | Time | Action |
| Order Entry Period | 9:00am - 9:08am | The client can place new orders, modify / delete the orders. The order entry can stop randomly between 7th and 8th minute. |
| Order Matching & Confirmation Period (can be called Price Discovery Period) | 9:08am - 9:12am | The exchange arrives at the Opening Price, trades the matchable orders @ Opening Price. |
| Buffer Period | 9:12am - 9:15am | Used as transition period between pre open and continuous trading session. |
| Normal Market | 9:15am - 3:30pm | Normal Trading resumes. |
