To be included and confirmed on the blockchain, a given transaction must be mined. To this end, each transaction includes a small ETH tip for the first miner that incorporates it. Because Ethereum smart contracts require variable amounts of computational complexity (GAS), most users interface with this tip by setting a GAS price. Transactions are mined on a first-come, first-serve basis, meaning that higher gas prices are generally mined faster; however, GAS prices fluctuate with network activity, and predictions for time to confirmation made by wallets are not always accurate.