True enough, Wolfgang - talking about oil running out soon is a kind of shorthand. It's a way of saying that, before very long, it will get too expensive to use in the way we use it, so we either have to stop doing the things we use it for, or find alternative ways of supplying the energy we need.

"...within the lifetime of many of the present population", writing in 1971 that means by the middle of this century. That still seems a reasonable estimate for a time by which we will have used up the bulk of the economically available oil and natural gas.

I'd imagine that in saying "The energy problem is not primarily a matter of depletion of resources in any global sense" Holdren might have been taking ointo accountb the fact that there are potentially excellent alternatve sources of energy, even witjhout oil.