Whenever you buy, breed, and create or cancel an auction, your request gets sent to miners on the Ethereum network who crunch the numbers and confirm the transaction (thank you, miners!). For that service the miners receive a network fee paid by the person submitting the transaction request (please note that entire fee goes to the miners, not us!). That fee, sometimes written as “Tx fee,” is determined by two factors: the “Gas Price” of your transaction and the amount of gas used to process it.