Why did PDN rise in Australia yesterday?, page-7

No ridicule, but perhaps you don't quite understand how the opening (and closing) auction works? It's an auction, and people put their bids in, for both the buy and the sell side. They try to outbid each other in both directions, and the matched price (listed on Commsec as "Indicative Price") is what the actual opening trades will trade at. That takes into account the number of buy and sell bids/offers that match up and based on the balance of numbers, what price they match at.

So the buy at 21c will actually trade at whatever the opening price is - currently indicated to be 18.5c

His price on that bid is 21c purely so he can be on top of the pile of buys, and get his order filled. Of course, if somebody else comes along and outbids him to move to the head of the queue, he may have to increase his bid, depending on the number of shares that "match up".

These days, most of the orders are worked out by the trading computers, so they "know" exactly where to put their bid and for how many shares.