Cryptocurrencies such as Bitcoin rely on a ‘proof of work’ scheme to allow nodes in the network to ‘agree’ to append a block of transactions to the blockchain, but this scheme requires real resources (a cost) from the node. This column examines an alternative consensus mechanism in the form of proof-of-stake protocols. It finds that an economically sustainable network will involve the same cost, regardless of whether it is proof of work or proof of stake. It also suggests that permissioned networks will not be able to economise on costs relative to permissionless networks.