The duration an additional 8 gallons of gas will last in a vehicle largely depends on several factors, including the vehicle's fuel efficiency, driving conditions, and the driver's habits. On average, if a vehicle has a fuel efficiency rating of 30 miles per gallon (mpg), an additional 8 gallons of gas would typically last around 240 miles. This calculation assumes standard driving conditions and a consistent speed.

The reason for this estimate lies in the relationship between fuel efficiency and the amount of fuel consumed. Fuel efficiency is measured in miles per gallon, which indicates how many miles a vehicle can travel on one gallon of fuel. Therefore, the more miles per gallon a vehicle achieves, the longer the fuel will last. For instance, a vehicle with a fuel efficiency of 40 mpg would travel 320 miles on 8 gallons, while a vehicle with a fuel efficiency of 20 mpg would only travel 160 miles on the same amount of fuel.

Data from the U.S. Environmental Protection Agency (EPA) provides a basis for these calculations. The EPA's fuel economy estimates are based on standardized test procedures that simulate real-world driving conditions. According to the EPA, the average fuel efficiency for new vehicles in the United States is approximately 25 mpg. This means that, on average, an additional 8 gallons of gas would last around 200 miles, which aligns with the estimate provided earlier.

It's important to note that actual fuel consumption can vary significantly from these estimates due to factors such as traffic conditions, weather, and the driver's habits. For example, aggressive driving, idling, and carrying heavy loads can all decrease fuel efficiency and, consequently, the distance an additional 8 gallons of gas will cover. Additionally, vehicles with larger engines or those that are not well-maintained may have lower fuel efficiency, further impacting the duration of the fuel.

In conclusion, while an additional 8 gallons of gas can generally be expected to last around 240 miles on average, this estimate can vary based on the specific vehicle's fuel efficiency and driving conditions. The EPA's fuel economy data serves as a useful reference for understanding the expected range of a vehicle's fuel consumption.