The Bitcoin cryptocurrency allows entities in a peer‐to‐peer network to reach consensus about the state of the blockchain through a set of cryptographic algorithms and economic incentives. Bitcoin uses a proof of work system, but there are other consensus mechanisms used by other cryptocurrencies. The performance of a cryptocurrency depends on the consensus mechanism used. This paper presents the results of a comparative evaluation that has been conducted on various significant consensus mechanisms. The unique characteristics, as well as drawbacks of each mechanism, are highlighted, together with their applications. The mechanisms are also classified into major types and those types are evaluated elaborately. The paper concludes with a discussion of the open challenges related to the available solutions.