# SurplusMinter [SurplusMinter](https://github.com/zkBob/zkbob-contracts/blob/master/src/minters/SurplusMinter.sol) smart contract is responsible for aggregated CDP protocol fees and interest collection. ### Key concepts ### Realized interest Certain fees collected by the protocol can be expressed as a realized interest. Such fees are collected in existing BOB tokens, obtained from liquidation fees and debt repayments. Protocol governance can withdraw these tokens as per their decisions. ### Unrealized interest Certain fees collected by the protocol cannot be expressed in existing BOB tokens, as they have not been truly repayed yet. Such fees include stability fees accumulated on active vaults, that haven't been yet repayed by vault owners. Protocol governance can withdraw those unrealized BOB tokens by minting them in advance, since any unrealized is expected to eventually converge to the realized one. ## Methods TBD --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://bob-docs.zkbob.com/bob-cdp/technical-docs/smart-contracts/surplusminter.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.