(According to Austin Family Magazine)
1. The first person who calls "shotgun" gets to ride in the front seat next to the window.
2. "Shotgun" must be spoken loudly enough to be heard by at least one witness.
3. A person may only call "shotgun" for one way of a trip.
4. "Shotgun" must be called while outside of the vehicle. (No arguments or calls inside the car).
5. The owner of the vehicle may make up his/her own rules for "shotgun" and is the final judge.
6. If a passenger in the "shotgun" seat leaves the car for a break, the break can not last more than five minutes or that passenger will lose the "shotgun" position. Long lines at the restroom are part of the five minutes.
7. Crossing any country's border changes the "shotgun" claims. So going into Mexico or Canada would change who owns "shotgun," but going into Oklahoma does not (go figure).
8. The "shotgun" passenger has responsibilities such as: pumping the gas, spotting speed zone signs for the driver, spotting radar on the side of the road and spotting law enforcement officers for the driver.
9. All ties for "shotgun" shall be decided by one round of "rock, paper, scissors."
10. To avoid arguments inside of the restaurant, all calls for "shotgun" must be made in full view of the vehicle by the passengers.
The full set of Official Rules & The Website of Shotgun can be found HERE.