Final answer:
A contract where a buyer agrees to purchase all of their required gasoline from a seller at a set price for a specific period is known as a requirements contract.
Step-by-step explanation:
The situation described where Sigmund enters into a contract with Carl to purchase gasoline at a set price of $2.50 per gallon for the entire year of 2011 is an example of a requirements contract. In such a contract, Sigmund is the buyer who agrees to purchase all the gasoline he requires from Carl, the seller, throughout a specific time period, at an agreed-upon price. This type of arrangement is common in business settings, especially when there's a need for a predictable supply chain, and both parties want to hedge against future price fluctuations.