Should fill it immediately if your ask is the same as a current bid.

In other words someone is selling a bc at 117, and you put in an order at 117 (same amount of bc) it will get filled.
If you place an order at 116 though- the order will be pending until someone wants to sell at 116.

Currently, you can buy 1 bc at S$117.95 which is about USD$93.77 or a 1.59% premium over the mt.gox USD rate, but still below the S$119 mt gox rate.

David