Market regulator likely to release consultation paper within a week as traders raise concerns over sharp price differences during the Closing Auction Session
New Delhi: The Securities and Exchange Board of India (SEBI) is considering a major change in the way derivatives contracts are settled at expiry, following concerns raised by traders, brokers and other market participants over the recently introduced Closing Auction Session (CAS) mechanism.
The market regulator is expected to issue a consultation paper within a week proposing changes to the methodology used to determine the settlement price of derivatives contracts.
The move comes after market participants reported sharp price movements and significant differences between prices discovered during the CAS and prices prevailing during regular trading hours, particularly on expiry days.
Why SEBI Is Reviewing the CAS Settlement Mechanism
The Closing Auction Session was introduced from August 3 with the objective of improving the process of determining closing prices.
Under the current framework, the closing price discovered through the CAS also becomes the basis for determining the settlement price of derivatives contracts at expiry.
However, market participants have raised concerns that the CAS price can sometimes differ significantly from the price at which a stock or index was trading during normal market hours.
These differences can become particularly important on derivatives expiry days, when futures and options positions are settled based on the prescribed settlement methodology.
Traders have argued that unexpected movements during the CAS window can increase volatility and affect the final settlement value of derivative positions.
20-Minute CAS Window Under the Spotlight
The CAS mechanism operates during a 20-minute window, from 3:00 pm to 3:20 pm.
The introduction of the mechanism led to considerable discussion among market participants over how prices are discovered during this period and how those prices are subsequently used for derivatives settlement.
One of the key concerns is the possibility of a significant gap between the price prevailing before the auction and the final closing price determined through the CAS.
Such differences can have a direct impact on traders holding futures and options positions close to expiry.
Why Derivatives Settlement Price Matters
The settlement price is extremely important in the derivatives market because it determines the value at which contracts are finally settled.
For traders holding large positions, even a relatively small movement in the underlying index or stock can result in substantial gains or losses.
Therefore, the methodology used to calculate the final settlement price needs to be transparent, predictable and resistant to unusual price movements.
The current debate has centred on whether the CAS-derived closing price should continue to be used directly as the derivatives settlement price, or whether another methodology should be adopted.
BSE Sensex and NSE Nifty Showed a Notable Difference
The concerns became particularly visible after differences emerged between the closing performance of the BSE Sensex and NSE Nifty on an expiry day following the implementation of CAS.
On one such expiry day last month, the two benchmark indices showed a difference of around 0.31 percentage points in their performance.
The Nifty declined by 40 points, or 0.16%, to close at 24,396, while the Sensex gained 114 points, or 0.15%, to finish at 78,080.
Although the two indices track different baskets of stocks, the contrasting closing movements drew attention to the impact of the new closing-price mechanism and the broader implications for derivatives settlement.
SEBI Confirms Review of Settlement Methodology
SEBI said in a press release issued on Thursday that it has been reviewing the initial experience with the CAS mechanism and the feedback received from various stakeholders.
The regulator said that based on the experience during the initial period of implementation and feedback from stakeholders, it may propose certain changes to the methodology for determining the settlement price of derivatives contracts.
According to SEBI, a consultation paper on the issue is expected to be released in approximately one week.
The move indicates that the regulator is actively examining whether the current mechanism is working as intended and whether adjustments are required to address concerns raised by market participants.
SEBI Consults Brokers, FPIs and Mutual Funds
Following the introduction of CAS, SEBI held discussions with several categories of market participants to assess its impact.
The consultations included:
- Stock brokers
- Market participants
- Foreign Portfolio Investors (FPIs)
- Mutual funds
- Other stakeholders across the securities market
The regulator sought feedback on the functioning of the new closing-price mechanism and the issues emerging from its initial implementation.
One of the major issues identified during these discussions relates specifically to the settlement price of derivatives contracts on expiry.
What Could Change Under the New Framework?
SEBI has not yet announced the final methodology. However, the proposed consultation process could examine whether the existing linkage between the CAS closing price and derivatives settlement price should be modified.
One possibility under discussion is greater use of volume-weighted average prices (VWAP) from regular trading immediately before the CAS.
Stock exchanges have already made changes related to CAS and have considered using the VWAP of trades conducted between 3:00 pm and 3:15 pm to determine the reference price for stock and index futures.
If adopted as part of a broader framework, such a methodology could potentially reduce the impact of sharp price movements during the auction period on derivatives settlement.
However, the final mechanism will depend on SEBI’s consultation process and subsequent decision.
Why Expiry Days Are Particularly Sensitive
Expiry days are among the most closely watched sessions in India’s derivatives market.
Large numbers of futures and options contracts expire on scheduled expiry dates, making the final price of the underlying asset particularly important.
A sudden movement in the final settlement price can significantly alter the value of open positions.
For retail traders, institutional investors, proprietary trading firms and other market participants, even a small change in the settlement methodology can affect trading strategies and risk-management calculations.
This is why the CAS-related settlement debate has attracted considerable attention across the financial markets.
Market Participants Seek Greater Predictability
The central concern among market participants is not simply the existence of an auction mechanism but the link between the auction-derived closing price and derivatives settlement.
Market participants generally seek a settlement methodology that provides:
- Greater price transparency
- Better predictability
- Lower scope for abnormal price movements
- Efficient price discovery
- Reduced settlement-related uncertainty
- Greater alignment with actual market trading conditions
The proposed SEBI consultation paper is therefore expected to attract significant attention from brokers, exchanges, institutional investors and derivatives traders.
CAS: What Is the Closing Auction Session?
The Closing Auction Session (CAS) is a mechanism used to determine the closing price of securities through an auction-based process.
Instead of relying solely on the last traded price during continuous trading, the auction process allows eligible orders to participate in price discovery during the designated closing period.
The objective is to arrive at a closing price that better reflects market demand and supply.
However, because this closing price can influence several downstream calculations—including derivatives settlement—the design of the auction and the methodology used to determine the final price become particularly important.
What Happens Next?
SEBI’s upcoming consultation paper is expected to provide greater clarity on the proposed changes.
The regulator is likely to seek comments from exchanges, brokers, institutional investors, traders and other stakeholders before finalising any amendments.
For the derivatives market, the outcome could be significant because any change in the settlement-price methodology may directly affect how futures and options contracts are valued and settled at expiry.
Until SEBI announces a final decision, the existing framework will continue to apply.
Bottom Line
SEBI’s decision to reconsider the derivatives settlement mechanism comes at a crucial time for India’s rapidly expanding derivatives market.
The introduction of CAS was aimed at improving closing-price discovery, but concerns over price differences, expiry-day volatility and the direct use of CAS closing prices for derivatives settlement have prompted the regulator to review the framework.
If SEBI ultimately changes the methodology, it could mark a significant shift in the way India’s stock and index derivatives are settled at expiry.
For traders and investors, the upcoming consultation paper will therefore be closely watched, as even a small change in the settlement formula can have a major impact on expiry-day trading and risk management.
