Question: I am traveling to Oklahoma state in USA next week. I am driving my SUV but I have 4 friends going with me and one more person will join us in Oklahoma. I am wondering if there is any legal limitation on the number of passengers allowed in one car in Oklahoma. Not including the driver seat, my car has 4 seats but there is some space in the back of the SUV so someone could sit on that. I can't find anywhere that tells the law on number of passengers allowed in one car in Oklahoma.

Answer: 
The only likely legal limitation is that there must be a seat belt for every passenger.

Some states only require seat belts for passengers in the front seat, or under a certain age (such as 13).

But to be safe, make sure every passenger is buckled in, and you will have no problems anywhere in the U.S.

As per the [NHTSA summary](http://www.nhtsa.gov/staticfiles/nti/pdf/811458.pdf%E2%80%8E), the number of occupants in the rear seat cannot exceed the number of available safety belts. Including the citations of the relevant laws on pages 19, 29, 33, etc.
[The state of Oklahoma does not require rear-seat passengers to wear seat belts:](http://ok.gov/ohso/documents/Safety%20Belt%20Law%20NFO.pdf)

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> All drivers and front seat passengers ages 13 and older must have a safety belt properly fastened about his/her body at all times while the vehicle is being operated.
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This would imply that you can legally pile four people into the backseat and/or the cargo area. The only other laws I've been able to find concerning passengers and where they can ride either apply to larger vehicles (with a seating of 15 or more) or concern whether passengers can ride outside the passenger compartment (short answer: in the bed of a pickup truck or in a parade, otherwise no.)

If you are passing through any other states on the road-trip, the [Governors' Highway Safety Association](http://ghsa.org/html/stateinfo/bystate/index.html) has a good collection of summaries of each state's traffic laws, including seat belt laws.