Every blockchain transaction has a non-refundable network cost, even if it fails. Validators use their resources to determine a transaction's outcome, relying on their own computers to verify and process transactions without a central authority.
The specific token required to cover these fees varies depending on the network being used.
Here is a list of the networks supported by Uniswap along with the tokens used for network costs:
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Ethereum - ETH on the Ethereum network
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Unichain - ETH on the Unichain network (note that Uniswap Labs receives a portion of network costs paid on Unichain transactions)
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Arbitrum - ETH on the Arbitrum network
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Avalanche - AVAX on the Avalanche network
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Base - ETH on the Base network
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Blast - ETH on the Blast network
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BNB Smart Chain - BNB on the BNB Smart Chain network
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Celo - CELO on the Celo network
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Optimism - ETH on the Optimism network
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Polygon - POL (formerly MATIC) on the Polygon network
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World Chain - ETH on the World Chain network
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ZKsync - ETH on the ZKsync network
- Zora - ETH on the Zora network
If you are swapping these tokens for another type, you may not be able to use your full balance to swap because you will need enough of the token to pay for the network cost.
If you need a token to pay for network costs, consider the following options:
- Purchase the network token using the Uniswap Wallet or the Uniswap web app.
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Transfer a network token to your wallet from a protocol, wallet, etc.
- Bridge tokens to the network you are swapping on to pay for the network costs.
Learn more about how network costs are determined here: How is a network cost determined?