New Delhi, Oct. 23 -- Asia's oldest stock exchange has defied expectations that a shift in weekly index options expiry days would hit its volumes, instead chipping away at its rival National Stock Exchange's dominant market share, per early trends.

The weekly expiry day of NSE's index options contracts was shifted to Tuesday from Thursday effective 2 September, and of BSE's to Thursday from Tuesday from 4 September.

Market experts had expected that this would enable NSE to recoup market share from BSE thanks to an extra day-Friday, alongside Monday and Tuesday-as opposed to Wednesday and Thursday for Sensex options.

But early turnover trends data show otherwise.

NSE's data show that its share of equity options-on index and stocks-fell...