> For the complete documentation index, see [llms.txt](https://hub.bsvblockchain.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hub.bsvblockchain.org/wiki/blocks-and-the-blockchain/blockchain/orphan-block.md). # Orphan Block An "orphan block" is a well-formed block with valid proof of work which has been rejected by Miners and does not form part of the longest chain of proof of work. As the block in question has not been accepted, the Block Reward and the \[(transaction)] are no longer spendable on the difficulty wise-longest well-formed Blockchain. This phenomenon must be taken into account by mining pools that use any payout strategy other than "proportional". An orphan block often originates when two Miners produce a block around the same point in time. The time delay in propagating and accepting a block leads to Bitcoin SV nodes encountering scenarios where they need to select which of multiple blocks to accept as the most legitimate to include next in the chain. After a block is selected by the network, the other block is considered an orphaned block. Transactions in the orphaned block that were not included in the successful block, are re-included into the mempool as membership candidates for future blocks. In most cases the vast majority of transactions will be included in both, as propagation of transactions across the network is very efficient and both Miners are likely to have seen the same set. In other instances, orphan blocks may be generated when malicious nodes seek to reverse transactions by generating alternative desired blocks. This, they hope to accomplish through the utilisation of large amounts of hash power (see 51% attack). However, attacks intended to cause the deliberate orphaning of blocks are extremely resource-intensive and are largely infeasible. The blocks they generate generally end up being orphaned themselves. 1. See Also * Miner subsidy --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## 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, and the optional `goal` query parameter: ``` GET https://hub.bsvblockchain.org/wiki/blocks-and-the-blockchain/blockchain/orphan-block.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. 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.