Old engine oil as wood preserver

[The Natural Philosopher]

The conditions for rot are nutrient water AND air ...

Things don't rot in deserts. Nor do they rot at the bottom of bogs. There are a few anaerobic fungi, but not many.

[Roger Hayter]

There are huge numbers of anaerobic bacteria, but they need a substrate with a useful exothermic reaction in the absence of oxygen. Wood doesn't seem to provide this when oxygen is completely excluded. Or not unless other substances are available to play the same chemical role. Even bodies undergo limited degradation down to rather unpromising chemicals, like keratin when buried in bogs.