Adsense ad order

Hi,
Do you have information about the order of adsense ads. Do they choosen randomly(of course content related)? Or is there any rule like best paying ad served first on the order for example...
For example I have 3 ads in a vertical content ad and do they take place from left to right in order by their average cpc or something else?

Thanks

 

of course content related
you can't choose high paying first display

 

I know it is content related(as I wrote) but do they have any logical order inside the ad?

 

There used to be theories about the ads being served. Something like the highest paid ads served first... and that's why adding more AdSense ad blocks to a site reduces CPC since low paying ads must be served or something. It's 3AM and I really need my sleep... it might be somewhere on the forum. But it's all guessing as far as I'm concerned.

 

So "less is more" theory is probably true...