xjo - weekend charting and chat - 28 mar 2014, page-3

"According to the ASX Expiry calander, Thursday was the Expiry for 'All Individual Equity Derivatives', however volume was low, but Friday has much higher volume than average."

I believe the following explains the situation:

Expiry for Equity Options occurs at close of business on Thursday of Expiry Day. So, options become exercisable if they are in-the-money on COB.

Stock may have to be bought by the option seller on the next day in order to deliver. But until the last second of Options Expiry Day it is often not known whether an option is in-the-money or out-of-the-money.

This is quite different from Equity Options. (Which typically occurs the week before, but not necessarily.)

The Level at which the Index Options are exercised is determined by the Opening Price of the stocks underlying the Index Option at the Open on Index Options Expiry Day. Quite different from Equity Options.

This is why you will see a huge spike in volume on Index Options Expiry Day right at the opening, but not on Equity Options Expiry Day.

The difference lies in the timing when the expiry figure is determined.

Redbacka