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Gas is the fee paid for executing transactions on the Ethereum blockchain. Gas fees also help keep the Ethereum network secure. The price of gas is denoted in gwei (giga wei) 1 gwei is 1,000,000 (1 billion) wei or 0.000000001 ETH. Gas prices change constantly and there are a number of websites where you can check the current price. The faster the transaction, the more you will pay and the price difference can be quite substantial.