Orders execution and priority

Student said:

Hi all,

Went searching on the ASX on the rules on how orders are executed and couldn't find anything, so does anyone know where this sort of information is available?

For example, say two people (A and B) have bids of A: 10000, B: 20000 shares at $1. "A" placed the order first, "B" placed the order second.

Someone places an order to sell 10000 at $1. How is the order split between A and B?

Does it matter if both orders were placed at or before pre-open?

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Student said:

Thanks for the reply. In that case I'd like to ask how something eventuated today:

Prior to open I saw a bid for 35k at 0.17, and no sellers at 0.17

I place an order to sell 35k at 0.17. Market depth shows my order at 0.17, the buyers at 0.17 and no other orders.

So I wait until open.

But somehow, my order only gets part-filled at 0.17, the rest went to someone else.

Could it be that someone slipped in a smaller limit order at 0.165 and swiped most of the order at 0.17 at open?

Any ideas on how can I best avoid this in the future?

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