Gas fee

A gas fee is the cost paid by a transaction sender for the compute and

storage that the network performs on their behalf. The term comes from

Ethereum, where every EVM opcode has a fixed gas cost, and the total fee

is the gas used multiplied by the price the sender is willing to pay per

unit. Non-EVM chains use different terminology but charge for the same

underlying resources.

Gas limit, gas used, and price

A transaction declares a gas limit: the maximum amount of gas the

sender is willing to spend. When the transaction executes, the EVM tallies

the gas used as opcodes run. The final fee is:

fee = gas_used * gas_price

If execution would exceed the gas limit, the transaction reverts and the

sender still pays for the gas consumed up to that point. If it stays under

the limit, the unused gas is refunded.

This applies to every EVM chain that tx.taxi routes to, including

ethereum, base,

arbitrum one, optimism,

polygon, and bsc. The

transaction receipt records both the gas used and

the effective gas price.

EIP-1559: base fee and priority fee

After EIP-1559 took effect, EVM mainnets and most L2s split the gas price

into two components:

• Base fee: a per-block protocol-determined price. It rises when blocks

are full and falls when they are empty. The base fee is burned (on

Ethereum) or otherwise removed from circulation rather than paid to the

validator.

• Priority fee (also called the "tip"): an optional per-unit payment to

the validator on top of the base fee, used to incentivise inclusion.

A transaction sets a maxFeePerGas (the cap the sender will pay per unit)

and a maxPriorityFeePerGas (the tip portion). The effective gas price is

min(maxFeePerGas, baseFee + maxPriorityFeePerGas). Legacy transactions

that pre-date EIP-1559 still work; they just specify a single gasPrice.

Non-EVM analogues

Other chains charge for resources too, with different names.

• bitcoin and other UTXO chains charge **transaction

fees** measured in satoshis-per-vbyte. There is no per-opcode metering;

the fee comes from the difference between input and output values.

• solana charges a small fixed fee per signature plus

per-instruction compute units, with optional priority fees to

influence leader prioritisation.

• tron uses energy and bandwidth, which accounts can

obtain by staking TRX or by paying TRX directly.

• ton, sui, and aptos each

meter compute and storage in their own units.

Common gotchas

• A pending transaction with a maxFeePerGas below the current base fee

will not be included until the base fee falls. It may sit in the

mempool indefinitely.

• Setting a tight gas limit on an EVM transaction risks an out-of-gas

revert. The sender still pays for the gas consumed, but the intended

effect does not happen.

• Gas costs vary widely across chains. The same opcode count on

ethereum mainnet costs much more than on a typical

L2. Always check the chain you are paying on.

• "Gas" is shorthand. On non-EVM chains, prefer the chain's own term

("fee", "compute units", "energy") when reading native documentation.