(Bloomberg) -- The top 13 public crypto-mining companies sold the equivalent of all the Bitcoin they minted in October, plus a little more, while the digital asset posted one of its biggest rallies since token prices crashed last year.

The liquidation-to-production ratio was about 105% for companies including Marathon Digital Holdings and Core Scientific Inc., according to data compiled by industry trade publication TheMinerMag, meaning they sold Bitcoin from their holdings in addition to what was produced. That is significantly higher than the previous three months, when the ratio was 64%, 77% and 77% in July, August and September respectively. The ratio peaked at 390% last June amid the crypto market crash and surging power costs.

The sales came as the largest cryptocurrency soared to an 18-month high in October. Notably, some of the most formidable Bitcoin-holding miners increased sales of existing coins, with Hut 8 liquidating more than their monthly production amounts, according to the latest operational updates. 

Bitcoin mining is an energy-intensive process in which miners use specialized computers to validate transactions on the Bitcoin blockchain and earn rewards in the token. Historically, miners tend to sell more coins to either replenish their cash flow or capture higher prices in a rally. 

Bitcoin surged 28% to around $35,000 last month, bringing its year-to-date returns to more than 100%. That’s still below the record high of almost $69,000 reached in late 2021. Shares of miners including Marathon and Riot have also more than doubled this year. 

Besides the sharp rebound in Bitcoin prices, some of the miners are raising capital from Bitcoin sales in order to buffer the shock from the halving, a Bitcoin code update that will effectively cut mining rewards by 50% early next year. 

The halving changes the formula that governs the issuance of new Bitcoin released from the blockchain every four years and aims to maintain the cap of token supply at 21 million.  

©2023 Bloomberg L.P.