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Oxford Writing and Style Guide no longer recommending the Oxford comma
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've never been so vindicated. I am practically the only Oxford comma opponent I know. Lo siento, Henry Higgins, the damned thing is antiquated for general use and in no way phonetically represents the flow of the spoken word!

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So, I'm sure Chicago will still avail you. I'm not a fan of the Oxford style overall for personal use, but it's pretty contextual to the Queen's English in a lot of cases so I never expected to be.