There have been many transactions with apparently 0 mining fees (gas price set to 0) lately. Including from F2Pool BabelPool and SparkPool.

While miners had always been free to include any transactions, they did it only for their own transactions, and in that case, they are cases where such transactions come from the same person and get mined by 2 different miners which means it’s not linked. It’s also not related to flashbots since those transactions are sent to the mempool. And with the behavior of those senders (only minting gas tokens), it definitely looks like they don’t pay the transaction fees or that if they do, it’s a very low price compared to regular mining.

Is there an eip recently added for allowing this? If not, how such transactions are achieved? Is there a new service that launched for doing this with several miners lately?

  • Hi there. How do you know these transactions reached the public transaction pool? (Just trying to rule out these being mined in a dark pool... ) Commented Apr 26, 2021 at 21:03
  • @RichardHorrocks Etherscan adds a label to transactions that appear in a block without being detected in the mempool first and that’s not the case here. Also, when I posted the question this morning, it was still written on Etherscan in how much seconds they were mined after being seen in the mempool. That still seems strange because Geth and OpenEthereum sets a minimal gas price based on the average gas price under which transaction aren’t relayed to other nodes. Commented Apr 26, 2021 at 21:21
  • Understood. Interesting question! Commented Apr 26, 2021 at 21:27

1 Answer 1


These transactions have a null gas price because they are sent by the miner itself.

If we look at the transaction history of the address 0xBbed1c61b6E68c397b021C1274080A2005042C08 we see one incoming transaction of 100 ETH on 13 April 2021 coming from...F2Pool. This leads to think, without too much doubt, that this address belongs to F2Pool.

Why some transactions come from the same person and get mined by 2 different miners ?

Your post mentions two addresses sending these free transactions :

Transactions sent by this address are only mined by F2Pool, which makes sense because, as seen above, the address belongs to F2Pool.

Transactions sent by this address are in fact mined by two miners : SparkPool and BabelPool.

However, by doing a quick research we learn these two miners are closely related "partners".

From the BabelPool website :

Babel Finance’s Ethereum mining pool is technically supported by Spark Pool, which is a technology-leading comprehensive mining pool and the world's largest Ethereum mining pool.

Babel Finance will work closely with Spark Pool and mining partners to serve miners better through more financial innovations.

Spark Pool and Babel Finance are partnering together and looking forward to more collaborations in mining finance to protect the future value network

What's the purpose of these transactions ?

These transactions are very expensive in gas to the point that an entire block is reserved for them. That's because they mint a gas token named CHI which creates a large number of smart contract at the same time. On the other hand, when CHI tokens are burnt, the previously created contracts are destroyed (using the selfdestruct OPCODE) which frees storage and rewards the sender. This process allows to reduce transactions gas costs.

These miners are therefore accumulating gas through this CHI gas token, may be to sell it if the gas price increases.


Miners want to maximize their profit. Thus, they have developed some strategies. One of them is to mine blocks containing no transactions. In fact, when they receive a new candidate block, honest miners :

  1. download and validate the block
  2. remove the transactions that have been included in the block from their transaction pool.

This is time consuming.

This is why, in some cases, a miner only collects the hash of the newly broadcasted block before starting to mine the next block. Since the miner has not verified the transactions of the candidate block and has not updated its transaction pool, its new block must not include any transaction (in order not to take the risk of including transactions that have already been mined, which would invalidate the block).

Now what about those 1-transaction blocks ?

That's basically the same strategy which is applied, except the miner includes its own transaction which mints for free a large amount of CHI gas token. These ones can be viewed as an investment and sold if the average gas price spikes. Another important point to mention : it does not seem miners share their CHI tokens with the pool members (who are therefore losers on these blocks). So these blocks could be somehow attractive to the miner.

References :

  • I would rather say that such accumulation of tokens is behaving as if the person indeed has a way to mint gas tokens at a price below the sale price. But this doesn’t make sense for a miner as the most effective is just to create transactions with a high gas fees. Commented May 1, 2021 at 15:12
  • I also got a reply from F2pool claiming all those transactions are mined by chance. But I’m not really believing it and I’m receiving further answers. Commented May 1, 2021 at 15:13
  • And one more thing, how those transactions ended up on the mempool? Commented May 1, 2021 at 15:18
  • @user2284570 I updated my answer, providing more info about the reason behind these 1-transaction blocks.
    – clement
    Commented May 2, 2021 at 20:29
  • 1
    @GallAnnonim Thanks for your input ! I checked the history of 0x2f731c3e8cd264371ffdb635d07c14a6303df52a. We can see its first inbound transaction comes from 0xfCCfFEFe4b22c03044FE1Ed82A479c0bCb0944C9. If you then look at the first incoming transaction of this one you get 0xF5F8977348f592DB9773C373fEf5bE362D103776 as the sender which is clearly related to SparkPool. This is why I think the address you mention is about SparkPool (but I would need more evidence to say this for sure).
    – clement
    Commented Jun 20, 2021 at 9:17

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