At this point, not even the Oxford style guide:
As a general rule, do not use the serial/Oxford comma: so write ‘a, b and c’ not ‘a, b, and c’. But when a comma would assist in the meaning of the sentence or helps to resolve ambiguity, it can be used – especially where one of the items in the list is already joined by ‘and’:They had a choice between croissants, bacon and eggs, and muesli.
There are some cases where the comma is clearly obligatory:The bishops of Canterbury, Oxford, Bath and Wells, and Salisbury
I’m quite inconsistent in my use of the Oxford Comma as is. But it’s an ages-old institution, and ceteris paribus ages-old institutions should be changed only slowly and with great deliberation. Considering people have been bitching about the serial comma for — it seems — nearly as long as it has been around, and it isn’t here being universally banished, I’m not ready to stand athwart this just yet.
The one and only.