Our business is transporting patient, so gasoline is directly related to income. What is the correct account to use? Gasoline expense or cost of sales ( cost of good sold? )

According to your question, you are engaged in ambulance service. In such a situation the cost of gasoline is a direct expense. I would suggest you refer to a good text book where the topic of operating costing is discussed. I can quote one: Management and cost accounting by Colin Drury.