Updated 2019-10-01

Free Gas Networks

Transactions use computational resources so have an associated cost. Gas is the cost unit and the gas price is the price per gas unit. The transaction cost is the gas used * gas price.

In public networks, the transaction cost is paid in Ether by the account submitting the transaction. The transaction cost is paid to the miner (or validator in PoA networks) that includes the transaction in a block.

In many private networks, the validators are run by the network participants and do not require gas as an incentive to participate. Generally, networks that do not require gas as an incentive, configure the gas price to be 0 (that is, make gas free). Some private networks may allocate Ether and use a non-zero gas price to limit resource use.


We are using the term free gas network to refer to a network where the gas price is set to zero. A network with gas price of zero is also known as a zero gas network or no gas network.

In a free gas network, transactions still use gas but the gas price is 0 meaning the transaction cost is 0:

Transaction cost = gas used * 0 (gas price)

Configuring Hyperledger Besu for Free Gas

When gas is free, limiting block and contract sizes is less important. In free gas networks, we increase the block size limit and set the contract size limit to the maximum value.

1. Set Block Size

If you want to remove gas from consideration and don’t mind blocks potentially taking longer to be created, set the block size limit (measured in gas) in the genesis file to the maximum accepted by Truffle (0x1fffffffffffff):

"gasLimit": "0x1fffffffffffff"

If you are more concerned about blocks arriving on time and don’t have very expensive individual transactions, set the gasLimit to a value closer to the amount of gas your validators can process in the configured block time.

2. Set Contract Size

Set the contract size limit to the maximum supported size (in bytes) in the config section of the genesis file:

"contractSizeLimit": 2147483647

3. Start Besu with Minimum Gas Price of 0

When starting nodes, set the minimum gas price to 0:


Configuring Truffle for Free Gas

If using Truffle to develop on your free gas network, you also need to configure Truffle for free gas.

Similar to setting block and contract size limits to their maximum values for Besu, we set the transaction gas limit in Truffle to the maximum possible.


Besu does not implement private key management. To use Besu with Truffle, you must configure a Truffle wallet.

Update truffle-config.js

Update the truffle-config.js file:

  1. Set the gas price to 0:

  2. Set the gas limit for a transaction (that is, contract creation) to be the block gas limit - 1

    gas: "0x1ffffffffffffe"