While demand is based on consumer purchases, supply is most likely based on

the willingness of producers to supply a product.

Explanation:

Demand is the amount of units of a certain product or hours of service that the consumer is willing to buy from the producer, the supply is the ability or willingness of the producer to work those hours to give those services, or to produce and sell those products, that is why supply is based on the ability or the possibility of the producer to provide the product.