Gas expected to be $4.00 a gallon come spring

In the states, almost all cars use unleaded fuel and the majority of light trucks do, too. Most deisel vehicles in the states are clearly marked as such somewhere on the body. If you stick to cars, there's very little chance of "getting the wrong type". Now if you're trying to find high octane fuel, just buy a bottle of octane booster, though I question how you can afford the car that needs it yet not the gas.