In the Charging Estimator section on their website, they think that a Model competitor gets 21 mpg (https://www.tesla.com/models https://www.tesla.com/models) a

In the Charging Estimator section on their website, they think that a Model competitor gets 21 mpg (https://www.tesla.com/models https://www.tesla.com/models) and gas is $2.70/gallon, so I would expect it to be based on that.