Why did my gas fee spike even though the network wasn’t congested?

[ed]

It’s one of the most frustrating things for crypto users:
You check Etherscan’s gas tracker — the network looks fine.
You send a transaction — bam, you pay 3–5x the expected gas.

So, what’s going on?

1. Base Fee vs. Priority Fee (EIP-1559 refresher)

Ethereum’s current fee model splits your payment into two parts:

Base Fee — Adjusted automatically by the network based on demand; burned after the transaction.

Priority Fee (Tip) — Paid to miners/validators as an incentive to process your transaction faster.

A low base fee doesn’t always mean you’ll pay less overall — your priority fee can still spike.

2. Causes of Unexpected Gas Spikes
   a) MEV Bots Suddenly Flood the Mempool

MEV (Maximal Extractable Value) bots constantly battle for profitable transactions like liquidations, arbitrage, or NFT mints.

Even during “quiet” network times, a bot war can cause temporary local congestion that pushes priority fees way up.

b) Wallet Defaults Are Overestimating Fees

Many wallets (MetaMask, Rabby, Trust Wallet) auto-set a safe max fee to ensure your transaction doesn’t get stuck — but that can overshoot actual requirements.

c) Misleading Gas Trackers

Gas trackers show average base fee, not the exact fee for the block you’re targeting.

If your transaction gets placed in a block with sudden activity, you might pay a lot more.

d) “Gas Wars” on Niche Contracts

A hyped NFT mint or memecoin launch can cause localized congestion for just one contract.

Your transaction to that contract competes in its own mini-auction.

3. How to Avoid Surprise Gas Fees

Use etherscan.io/gastracker or txpool dashboards to check priority fee trends before sending.

Manually set a max priority fee in your wallet to prevent wild overspending.

If possible, send during predictable low-traffic windows (UTC 2–4 AM often has lower fees).

Pro tip: Some advanced wallets let you “snipe” low-fee blocks by queuing transactions for future inclusion — handy if you’re not in a rush.

Bottom line

Gas fees are more like an auction for block space than a flat rate. Even if the freeway looks empty, a sudden stampede of Lamborghinis (a.k.a. MEV bots) can still make your ride a lot more expensive.

[jacson4]

This makes so much sense — I always wondered why gas trackers said “low” but MetaMask still charged me double. Those MEV bot wars really are the hidden gas killers.

[Nahid10]

Great breakdown . The “mini-auction” around specific NFT mints explains so many painful nights. Manual priority fee settings are underrated, saved me tons of ETH already.