Gas fees are determined by the amount of ‘congestion’ on the Ethereum network, recorded at the time of a transaction. Because congestion is determined by the number of transactions happening on the network at a given time, gas fees vary. Therefore, lower gas fees occur when the lower amount of transactions are happening on the specific network, while higher gas fees occur when the network is completing more transactions.
Learn how to adjust gas fees on Coinbase Wallet.
Learn how to adjust gas fees on MetaMask.