xatt has an auction system where you can bid for limited powers.
Before bidding on a power, read the auction rules as stated on the power auction page.
In this auction system, each bidder bids the current minimum value on the quantity of powers they wish to acquire (up to 80 powers), and at the end of the auction everyone will pay the current minimum value. If you win an auction, the xats will be automatically deducted and the powers will be placed on your account.
Note: You may increase your bid as the minimum value increases. However, you cannot reduce the quantity of powers that you are bidding for.
If the auction is for 8000 powers and at the end of the auction the minimum bid is 200 xats, everyone who bid 200 xats or more will win the auction and get the powers for 200 xats each. Everyone who bid less than 200 xats will not win the auction, but they will also not lose any xats.
It depends on what you want to achieve. For example, if there are 500 clear powers up for auction: