 What happens to transactions in stale blocks, or blocks that are basically orphaned or end up on a minority chain? Well, if any transactions that were in that block, if they weren't in the block that replaced it, they go back in the mempool. So every node will remove the transactions that actually did get mined into a block. If a block gets orphaned, or the chain reorganizes around that block, then all of the transactions go back in the mempool, unless they're on the other chain. Generally speaking, if you have two blocks that get mined near simultaneously, one of those blocks will be successful, the other one eventually will get orphaned. As a result, that block will have its transactions replayed, but most of those transactions will coincide. Two blocks mined to the approximate same time may have 90% of the same transactions, 95% of the same transaction. Really, only the 5% that didn't get put into the alternative block are the ones that need to go back in the mempool for inclusion in the next block. Nothing gets lost, though. They just wait a bit longer. It's the same as if they hadn't had sufficient fees. If they hadn't been picked in that round, they will get mined eventually. June asks, I submitted a small transaction to send BTC to another address, and it has been pending for over a week now. I was testing to see if I would be able to send a transaction for the lowest fee of one Satoshi per byte. I'm afraid the transaction is stuck and cannot be double-spent with a higher fee, because the wallet gives me an error that it's in the mempool. Is there anything I can do to cancel my transaction on my end, or will I have to wait until it drops off the mempool in order to resend it with a higher fee? Thank you, Andreas. All right, June, great question. This is a really important question that affects a lot of beginners in Bitcoin. Really, what you're experiencing is a combination of a mempool that is a marketplace for transactions, where if you want your transaction prioritized, you're competing against others. Your own wallet may have certain policies and approaches to how it does transactions that may not be ideal. First of all, is it possible to send a one Satoshi per byte fee? Absolutely. Every single transaction I do, I pay one Satoshi per byte. I haven't paid more than one Satoshi per byte since February, so it is absolutely possible to send with one Satoshi per byte. Those transactions do get confirmed. However, in order to do that, I'm using a wallet that gives me options for managing the narrow cases, which happen one in ten transactions. I'll have a problem where it gets stuck, just like you've experienced here. When that happens, my wallet gives me two ways to unstick that transaction. The first one is called replace by fee, which means that my initial transaction is marked as RBF, meaning it is able to be replaced by a transaction spending a higher fee. It's not the final version of that transaction, if you like. There may be subsequent transactions that spend it with a higher fee. By doing that, that is just an extra signal to the miners, because the miners can choose to take a double-spent, higher fee transaction if your wallet can create it, regardless of whether you say it is replaced by fee or not. Miners will always use an algorithm that maximizes their profit. If they have two transactions, and one of them is a double-spent of a previous transaction with a higher fee, and that first transaction hasn't been confirmed, they'll take the higher fee. It doesn't matter if you're signaling RBF or not. Although some miners will look for RBF transactions, and the algorithm will treat them favorably if there's a replacement transaction. Really, what that's about is your wallet knowing how to manage that double-spent situation. That's one technique replaced by a fee. The other technique is called child-pays-for-parent. Again, this is not like a magical feature that's instructing the miners what to do. It's simply recognizing that miners will always maximize their profit and take the transaction or chain of transactions with the highest fee. Child-pays-for-parent says, my first transaction doesn't have enough fee per byte to confirm. What I'm going to do is chain a second child transaction that depends on spending the first one with a higher fee. What miners will do in their algorithm that selects transactions from the men pool, is they don't look at how many Satoshi's per byte in each transaction. Instead, they look at how many Satoshi's per byte in each chain of unconfirmed transactions. If you have a parent and a child, their total Satoshi's fees are divided by the total bytes, so that the miner can make a determination in their best interest, that if they confirm both of them together, they can get a better Satoshi per byte rate than if they don't confirm the first one, because you can't confirm the second one. Child-pays-for-parent, again, is a technique used by the wallet that recognizes that miners' transaction selection algorithms will be based on maximizing their profit. The wallets I use, Samurai Electrum, for example, tend to support these capabilities and allow me to do that. You can actually construct a child-pays-for-parent transaction if you construct it manually. If your wallet isn't allowing it. Back to your question, Jen. You said, you're afraid the transaction is stuck and cannot be double-spent with a higher fee, because the wallet gives me an error that it's in the men pool. That doesn't mean it cannot be spent by a higher fee. That means your wallet is refusing to do it. If you manually construct a double-spent transaction with a higher fee, using another wallet, for example, that supports that, it will go through, and you'll be able to nudge that transaction through the men pool. The way I do transactions is I always start with the absolute lowest fee possible. I mark the transaction as replaced by fee. I let it sit in the men pool. If it's urgent, for example, if I have a 15-minute window, because I'm doing a retail transaction, I'm going to check on it and see how it's sitting in the men pool, and I might bump it immediately. If I see that I miscalculated the fee. But if it's not urgent, and I have a day, for example, today is the 1st of September. I'm about to run payroll, and payroll in my company is Bitcoin. I'm about to do a whole bunch of transactions. In fact, there are multi-recipient transactions where I pay my staff in Bitcoin. Those transactions don't need to get it in the next 15 minutes. As long as it goes through today or early tomorrow, it's good enough. That means I have a 144 block window to get them through, which means I don't need to worry about the fee. One Satoshi per byte will work. If, by some weird coincidence, the moment I decide to do that, there is a massive rally or the men pool gets absolutely chock-full of transactions, I might have to bump it. I'm going to replace my fee. I'm also going to use Child Pays for Parents, which sometimes works faster to confirm that transaction and get my payroll through.