The duration that 275 gallons of oil lasts can vary based on several factors, including the size and efficiency of the heating system, the climate, and the insulation of the building. On average, a typical residential oil heating system may consume around 4-7 gallons per day during the winter months. Based on this estimate, 275 gallons of oil can last approximately 39-69 days. However, it's important to note that individual usage can vary significantly, so it's advisable to monitor your oil consumption and adjust accordingly based on your specific circumstances.