The worst imaginable scenario is World War III, but production would perhaps only be cut in half.

That's a very optimistic "worst imaginable" nuclear world war if I ever saw one!

For a world wide financial collapse scenario look to the Former Soviet Union's experience. (Perhaps you can post the USSR production graph?)

From Mazmascience's energy browser (based on BP data)

[Edit: deleted graph as its creator Jonathan Callahan has posted the info below]

I just wish the fools try to maintain "status-quo" until they realize they don't have enough oil for wars. I wish, things unfold like its mentioned in the Long Emergency. But I'm scared to think of what the various nations will do given their latent nuclear weapons. They don't need (much) oil for firing these, anyway.

A self-destructing pakistan is good enough to start WWIII.