Actually, it depends on the efficiency of the vehicle, and how many passengers both are carrying. Vehicle MPG drops as the load of the vehicle goes up (more passengers), and it also takes longer to drive. Yes, private planes would be less efficient, as many of them take only a max of 10 to 12 passengers, but in many cases, the number is about half of that. However, commercial jets which carry many more are more efficient than cars. And, it could actually be a tie, or the plane could be more efficient, as a basketball team takes 15 players, but then you also have to factor in the coaches, and the various support personnel the team requires.