Cardano uses a proof-of-stake protocol named Ouroboros;[13] this is in contrast to Bitcoin and Ethereum, which use proof-of-work protocols.[14] Proof-of-stake blockchains use significantly less energy than proof-of-work chains.[14] In February 2021, Hoskinson estimated the Cardano network used 6 GWh annually, less than 0.01% of the 110.53 TWh used by the Bitcoin network as estimated by the University of Cambridge.[15][16] Cardano reached a market cap of $77 billion in May 2021 and was solidified its position as the biggest proof-of-stake cryptocurrency.[17][18]