A plane like a Boeing 747 uses approximately 1 gallon of fuel (about 4 liters) every second. Over the course of a 10-hour flight, it might burn 36,000 gallons (150,000 liters). According to Boeing's Web site, the 747 burns approximately 5 gallons of fuel per mile (12 liters per kilometer).
This sounds like a tremendously poor miles-per-gallon rating! But consider that a 747 can carry as many as 568 people. Let's call it 500 people to take into account the fact that not all seats on most flights are occupied. A 747 is transporting 500 people 1 mile using 5 gallons of fuel. That means the plane is burning 0.01 gallons per person per mile. In other words, the plane is getting 100 miles per gallon per person! The typical car gets about 25 miles per gallon, so the 747 is much better than a car carrying one person, and compares favorably even if there are four people in the car. Not bad when you consider that the 747 is flying at 550 miles per hour (900 km/h)!
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