IDL?

I look at the IDP (International Driving Permit) as "insurance" and following the law even though it might seem excessive. We've never been asked to present it at the car rental businesses in Costa Rica or Palermo, Italy.
Here is AAA's link. Btw, I think we paid only $25 @ 8 months ago. The link says $20. . . You don't even have to go to a AAA office but can mail everything in.
https://www.aaa.com/vacation/idpf.html

The IDP--permit, not license--translates your license into a common format. Some countries require it, some don't

It's not so much that the rental agencies require it but the police may if you are stopped. No IDP in some countries and you could be in big trouble.

Think of it as a $20 insurance policy.

Being asked for it has nothing to do with it being a requirement. You need it if you are pulled or have an accident. Some have reported being denied a car without it, and I believe them.

Some European States require it by law, others don't.

Italy does require it (art. 135 of the Italian Vehicle Code) and the minimum fine for not having it is €408.

The rental agency couldn't care less if you have it or not. I've never been asked by the rental agencies either.

But I was pulled over twice by the Carabinieri for a random check in the past 10 years (last time this past July 2024), and they did ask to see it.

So the choice is yours. Either pay $20 to the AAA (+$9 if you need them to take your photos) or pay the Carabinieri or the Polizia €408 if you get pulled over.

Here is what the US Embassy in Italy says:

https://it.usembassy.gov/u-s-citizen-services/local-resources-of-u-s-citizens/transportation-driving/

The clerk at the rental agency may or may not require that you show them your IDP in addition to your DL. That does not negate your obligation to have one if required by law in the country you are in. We have had to show it to police twice, once at a road block in France, and once in Italy. Keep in mind, that in some countries you would not only be subject to a fine, but the car could be seized (since you would be considered an unlicensed driver), and in an accident your insurance would be void for the same reason.

I was asked for it at a rental desk in Civittavecchia, after a cruise.

I realize that you are just asking a civil question, but I am reminded of some assigned novel in High School (1967) where an American held up his passport and expected the rebels to stop shooting while he crossed the street! “You not at home”, so there is little to be gained by trying to get a different answer.

I also look for the legally required safety equipment so I’m not charged for it upon the vehicle return.

I felt some doubt that Pseudoephedrine was actually illegal in Singapore, but I decided to remove it from my travel meds for just that trip!

I was driving near Fussen a few years back and came to a closed intersection. The officer came to the car and asked for my license. He spoke very little English and I spoke hardly any German. I showed him my actual license and the IDL. I then managed to make him understand I needed a new direction on my map to get around the road closure. Once he figured out what I was trying to say he showed me on the map where to go. I was very glad I had the IDL.

“Europe” isn’t really a unifying concept here because many countries specifically accept foreign licenses by country (list given), or foreign licenses in English, or foreign licenses in the Latin alphabet— whatever the national code says.

Some countries like Germany accept licenses of a certain international format, so in this case your Oklahoma license would work (and Laurie Beth’s Minnesota license would also work) but Roberto’s California license would not.

I was asked for it at a rental desk

I have heard of others being asked in Italy at time of rental, so perhaps the most compelling reason to get one in Italy so as not to upset the trip there and be stranded.

So country by country and depending upon your state license, but usually not a requirement in the most popular countries in Europe.

On a related note, Avis requires the renter to show proof of being licensed for at least 6 months. I’ve been licensed for over 45 years but just renewed it in October so I took my expired license too. Then the Avis associate at the rental office never asked to see it. Oh well!

Some countries like Germany accept licenses of a certain international
format, so in this case your Oklahoma license would work (and Laurie
Beth’s Minnesota license would also work) but Roberto’s California
license would not.

I'm not a legal expert, but as far as I can tell a license from Oklahoma or Minnesota is not valid in Germany without an IDP.

Come to think of it, even at home, the last time I was asked by the police for my driver's license was after I was rear ended in about 1990. Guess I don't need my DL either since I've never needed it.

The only time we were every stopped by the police in many trips we were asked for the IDL and the cop was visibly disappointed that we had it as he was winding up. I think it might also cause problems with your insurance in an accident if you were not properly licensed with it. You will definitely be asked to show it if in an accident. It is cheap. It is ridiculous that it needs to be constantly renewed; once should be enough. But it is cheap and required so we always carried it.