I read many topics, but still it is not clear to me. I have been 3 months in Thailand on a non-immigrant "O" visa. I left Thailand 16 january.

Do I have to wait now 90 days before I can ask again for a 3-months non-immigrant visa?

There is no limit on the amount of time you can be in the country in any period of time.

There was a rule that limited the number of days using visa exempt entries. But it has gone away. There has never has been a rule that limited time on visa entries.

Thank you for your quick response!

Makes me quiet again.

Sometimes I am afraid that some country will throw my country (the netherlands) off the first place on earth of having the most ridiculous rules....

So I can fly in and out of the country every 30 days with no limit now?

Yes

The 90 day rule went away Nov. 25th last year. But a border run will only give you 15 days instead of the 30 you still get by flying in..