What type of contract is formed when a customer fills up at a self-service gas station?

The correct answer, an implied in fact contract, is appropriate in the context of a self-service gas station because such contracts are formed through the actions of the parties rather than through explicit written or spoken agreements. When a customer fills up their vehicle with gas at a self-service station, they are demonstrating an intent to purchase fuel and pay for it by actively engaging in the service the station offers.

In this scenario, the customer's conduct indicates acceptance of the terms typically associated with purchasing gas (i.e., the price displayed on the pump, the nature of the service, and the expectation of payment). There is no formal agreement or negotiation occurring; rather, the customer's actions imply consent to engage in the transaction.

This self-service model naturally leads to the creation of an implied contract, as the conditions of the sale are understood and accepted by both parties (the customer and the gas station) through their actions rather than explicit communication. The other options—express contract, bilateral contract, and quasi contract—are less applicable in this context because they either require an explicit agreement or do not fit the scenario of typical consumer transactions at a self-service station.