There is no solid evidence, because the Saudi's are deliberately witholding the information. But I've added the time series of claimed OPEC reserves to Prof Goose's post at the top. If you want to bet your future on the idea that these are truthful statements by people carefully and scientifically making their best ongoing estimates of their reserves, be my guest. I can't imagine any way that hypothesis could explain those time series. The hypothesis of a bunch of liars trying to outbid each other for quota seems very consistent with the data. If they don't want to be called liars, they can damn well open up their records for audit. I think they are liars.
If they don't want to be called liars, they can damn well open up their records for audit. I think they are liars.

I don't like that logic wherever it appears.
For example, Stuart, I am beginning to wonder whether you might be engaging in some perverted activity in the privacy of your own home. Sure, you can deny it, but that's what all perverts do. If you don't want to be called a pervert, you can damn well let me install surveillance cameras in your home so I can monitor your activity 24-7. I think you're a pervert.

See how slick that works?

JD, is the world dependent on Stuart's perversion?  (lord knows I am, but is the rest of the world?)
It is true that the more important something is, and the more people are affected by it, the more transparency should be required.

I mean, should we know about the state of food production in the world? The state or drinking water? The pollution levels in the air, soil and water?

But sadly, even in these domains we don't have all the information...

the more transparency should be required

Required by who? Here's the question nobody is answering: What if the Saudis just say "No, we're not going to provide transparency. You're just going to have to trust us." What then? What's the "or else"?

that is exactly what they are doing... and may in all likelyhood keep doing. Leaving us A) without any hard data B) without any oil (unless of course you actually believe Ali Baba and the Forty Thieves).
As you live, so you judge.
That is a ridiculous analogy. Would open their records for audit (of the resource the world economy and is most dependent on!) violate their privacy? would that let us know what they do 24-7?. For the same reason you need transparency in the corporate world (would you buy stocks of a company that doesn't disclose it's accounting books?), you need it even more in the energy world.