> For the complete documentation index, see [llms.txt](https://cvnnt.gitbook.io/documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cvnnt.gitbook.io/documentation/how-it-works/gas-model.md).

# Gas model

In the UTXO model it is impossible to partially refund a fee for transactions that don’t use up all the gas while gas model for Ethereum works by overestimating the cost of contract execution and after execution refunding the remaining fee amount by crediting it back to the spending account balance. To eliminate this challenge, Covenant utilizes virtual gas representation along with Gasless model. 

### Covenant gasless model description

The Covenant system has its virtual gas representation for seamless EVM experience and to complement EVM systems. However, Covenant takes fees and commissions in tokens and assets that are native to the networks (e.g. network' native gas token, USDT/USDC tokens, etc.), integrated with the Covenant system:

Examples:

* BTC
* USDT
* USDC
* other native tokens and assets of the integrated network.

The user can choose one of the following ways to pay for a complex transaction:

*  Paying with a native token of the blockchain from which the user initiates the transaction.
*  Paying with a token from the transaction body. The user can pay for the complex transaction with the token being sent. The fee is included in the transaction body to be signed by the user.

E.g. a user depositing BTC pays all fees (Bitcoin fees and Covenant system commissions) in BTC. A user depositing Tron USDTs (for example, to buy BTC on Covenant system) pays all fees (Tron fees and Covenant commissions) in TRX or USDT.