New Stock Market Closing-Auction System Sparks Extreme Options Volatility

A newly implemented closing-auction system in stock markets is producing extreme price swings in the options market, creating and wiping out significant gains within minutes. The sharp volatility stems primarily from a structural mismatch in how cash equities and options markets close.

Stocks with tied derivatives receive their final prices through an auction process, while options continue trading concurrently. Because some expiring options trade at near-zero value, even slight movements in the underlying index can temporarily turn a worthless contract into a high-value asset before it crashes back down.

The effects of this mechanism were evident during the first monthly expiry under the new system at BSE Ltd. A ₹64,000 put option tied to a bank index traded at ₹1.70 at the start of the auction. Within 15 minutes, the price surged to ₹68.55—a jump of nearly 4,000%—before crashing back to zero.

Market participants noted that thinner liquidity at the BSE contributed to the severity of the swings. BSE recorded approximately ₹446 crore in closing-auction turnover on Thursday, compared to the National Stock Exchange of India Ltd, which saw ₹1,377 crore during its monthly expiry on Tuesday. The National Stock Exchange also experienced sharp moves, though they were muted relative to its smaller rival.

During Thursday's 20-minute auction window, the Sensex dropped sharply to 74,983.19, marking an almost 3% decline from its 77,182.91 level at the end of the continuous trading session at 3:15 p.m., before paring losses to close 0.7% lower. The BSE Bankex similarly indicated a 3.3% drop before recovering to close down 1.7%.

Maurya Ghelani, a derivatives strategist at Kai Securities in Mumbai, noted that the system effectively compresses an entire trading session's worth of risk into a few minutes, leaving little time to react for those positioned on the wrong side.

Ponmudi R, chief executive at local brokerage Enrich Money, described the market behavior during these windows as resembling a lottery ticket, noting that contracts can become worthless by the time traders realize a gain.

"Structural changes in market infrastructure, such as new closing-auction systems, require careful calibration to avoid unintended consequences in derivative segments. When liquidity is thin, timing mismatches between cash equities and options trading can amplify volatility and concentrate immense risk into narrow windows. Financial institutions, brokerages, and retail participants must exercise heightened caution and reassess their risk management frameworks during expiry windows to navigate these sudden market fluctuations effectively." — Dr. Shishir Gupta, Founder & CEO, StartupLanes