I can't give you a number, either, but it makes sense that as source rocks reach thermal maturity, more oil is being generated.
The rate of generation may be abysmally slow compared to our rate of consumption, but it is still being made.
Note: I am NOT saying oil is abiotic in origin, just that the same processes which generated the oil we tap today are still going on out there.
I doubt it; this is one big mother of a planet.