This question already has an answer here:

The main argument: which is advisable of the following two?

  1. A, B and C
  2. A, B, and C

Oxford (or serial) comma is useful to avoid ambiguities in phrases that involve lists such as the example given in this link. I tend to use it in long lists or that which could enclose conjunctions like 'and' or 'or' within them like so

The methods used include regression analysis, trial and error, and statistical inference.

However, how necessary is it when it concerns single-worded lists, especially when it concerns notational identifiers like A, B, C?

merged by tchrist Apr 1 '17 at 22:55

This question was merged with Should I put a comma before the last item in a list? because it is an exact duplicate of that question.

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