For me it depends on how many drivers there are and/or the distance your going, for short and med distances, one car = one driver, for long distances two drivers per car, for extreamly long distances a driver per car and a syphon, take the gas out of the car your going to ditch at a safe location when its at about half the tank of the other car to fill it up then keep going.. but thats only as a last resort if/when its needed