Consumer surplus measure the benefit buyers receive from participating in a market. In this example, John receives a $20 benefit from participating in the auction because he pays only $80 for a goods he values at $100. Paul,George,and Ringo get no consumer surplus from participating in the auction because they left without the album and without paying anything.
Consumer surplus is closely related to the demand curve for a product. To see how they are relate, let’s continue our example and consider the demand curve for this rare Elvis Presley album.