Miners generally select the highest-fee transactions, so when the mempool is congested, fees rise as users compete for limited block space.
Transaction fees from the mempool are part of miner revenue alongside the block subsidy, and become proportionally more important after each halving.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.
Keep learning
New to crypto, or filling in the gaps? Work through the essentials in Learn, browse every term A–Z, or see live prices for the coins these concepts power.