I believe my two title questions are the same (are they?):

Heretofore, what is the longest chain of orphan blocks (of N blocks), such that if someone didn't wait for N+1 confirmations, they may have assumed transactions to be completed when they were not.

For example, on the wiki's blockchain article, it shows orphan chains of two blocks (N=2). In this case, 3 confirmations would have sufficed to confirm transaction with absolute accuracy. https://en.bitcoin.it/wiki/File:Blockchain.png

I ask because it seems 120 confirmations is the gold standard, if you will, as generated bitcoins take that long to confirm. Most other transactions are considered irrevocable at 6 blocks, but what has been the minimum, thus far?

PS. Is this question even answerable!?


2 Answers 2


The longest orphaned fork was created due the "value overflow" bug occurrence, ranging from block 74638 to 74691 (so 53 blocks). Such a situation is unlikely to ever repeat though.

Other than that, as far as I remember 4 blocks were overwritten by some strange behaving miner (related question), but I might be mistaken.

In general, 6 confirmations is enough in most cases to prevent any double-spend attempts, and 120 confirmations is enough to give the developers time to release a fix for some major bug that might occur before the coin creation transactions are mixed in with everything else, creating a big mess.


Yes, the question is answerable, although it might be hard to get the data to answer it (you would need blockchains from a few very long-running, well-connected nodes that contained both the main chain and orphan chains).

I don't know the answer. As ThePiachu says, the longest orphan chain was 53 blocks, but I don't think any confirmed-on-one-chain transactions ended up unconfirmed on the other chain-- I don't think there were any double-spends across those two chains.

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