To write data onto a blockchain, computers (nodes) must spend electrical energy to run calculations. Users pay for this work via **Gas Fees**. Gas acts as the fuel for EVM transactions.
### How Gas Prices Fluctuate
Blockspace is limited. When thousands of users try to transact at the same time (e.g., during a popular NFT launch or market crash), they bid against each other.
* **Gwei:** Gas prices on Ethereum are measured in Gwei (1 Gwei = 0.000000001 ETH).
* **Prioritization:** Validators pick transactions with the highest gas prices first. If you set your gas price too low during peak traffic, your transaction will remain ‘Pending’ or get stuck.
### Gas Limit vs. Gas Price
1. **Gas Limit:** The maximum units of computational work you allow a transaction to perform (standard transfers take 21,000 units).
2. **Gas Price:** The amount of Gwei you are willing to pay per unit of computational work.
If you set a gas limit that is too low, the transaction will run out of gas and fail, but the network will still charge you the fee for the work completed.