Consumer Surplus - An Intro Set of Ideas
The graph at left shows a market demand function for a good and specifies a market price. Every unit of the good that is purchased is purchased only if the marginal benefit to the consumer of that unit - shown by the height of the demand curve at that point - exceeds the market price. For the 10'th unit for example the benefit of consuming the 10'th unit exceeds the market price. This is true so long as 50 units or fewer are purchased. For the 51'st unit the marginal benefit is less than the market price. In other words, for the 51'st unit the consumer surplus would be negative.

To Return to the consumer and producer surplus page in Prometheus please re-activate that window, perhaps closing this one. Alternatively you can link to the add-in page created for Producer Surplus by clicking on the ub logo to the right.