How long can a US Citizen stay on Bonaire with passport only????

I believe it is up to 90days if given permission by the proper authorities at the immigration office downtown.

14 days with no paperwork. If you plan on staying more than 14 days, you need to go to the immigration office downtown, and you can get an extension to 90, generally with no problem. You basically need to assure them that you are here for vacation/R&R, and not here to work.

If you need to work, it's a whole different kettle of fish.

We'll be here 92 days by the time we get our flight back. The immigration agent at the airport said "No problem" and stamped us for 90 days

Just a little happy update. I read this post and so went to the immigration office downtown today (as we're staying for 2 1/2 months.) The agent there looked at our passport and on the bottom right hand corner of our immigration stamp the number "90" had already been written in. The immigration officer at the airport had written that, maybe now it's standard procedure? She didn't ask us how long we're staying (but maybe it's on the paperwork I filled out on the plane?) That's all we needed; no need to go downtown after all. :-)