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Academic writing tips: Purpose and use of Oxford Comma

It is generally understood that commas can be used to separate items in a list. However, style guides tend to disagree about whether there should be a comma before the final ‘and’ or ‘or’ in a list. This is known as the ‘serial’ or ‘Oxford’ comma, and it is a subject of some debate. This article gives an overview of the Oxford comma and provides some guidelines about its use.

Purpose of Oxford comma: Removing ambiguity

Consider this sentence (which has no Oxford comma):

The solution contained a mixture of reagents, potassium nitrate and sodium chlorate.

What are the reagents here?

As written, they could be ‘potassium nitrate and sodium chlorate’ (meaning that the comma above is separating two clauses).

However, if this is actually a list of three things, then ‘a mixture of reagents’ will be referring to something else entirely and is considered an entity of its own, distinct from potassium nitrate and sodium chlorate.

So, which is it?

Without an Oxford comma, we have no way of knowing for certain.

The inclusion of an Oxford comma will remove ambiguity in this case:

The solution contained a mixture of reagents, potassium nitrate, and sodium chlorate.

This clearly indicates that the sentence contains a list of three things.

If the intention is instead to specify the two reagents, then the comma in the first version could be replaced with a colon (:), like this:

The solution contained a mixture of reagents: potassium nitrate and sodium chlorate.

In scientific writing in particular, it is very important to make sure that what you have written can be precisely understood. The Oxford comma can help with this.

Usage of Oxford comma: British vs. US English

As noted earlier, different style guides have different opinions, and the main split in this case seems to be between British and US English: the majority of US publishers insist on the use of the Oxford comma, while British publishers have varying opinions on this topic.

General works in British English (such as newspapers and fiction) tend to omit the Oxford comma. Indeed, it is even sometimes taught in British schools that using it is ‘wrong’. However, worldwide, academic publishers are more likely to recommend its use. This is because, as described, it can help to avoid ambiguity.

Deciding when to use Oxford comma

  • If possible, check with the style guide provided by your target journal, publisher or academic institution to ascertain their preference.
  • If a style guide is not available, then looking at recent publications is another way to find out.
  • If neither of these is possible, then, in scientific writing, it is usually safer to assume that you should include Oxford commas. 

Whatever you decide, make sure that you are consistent in your choice throughout a document: this also helps to avoid ambiguity.

When Oxford commas can create ambiguity

Sometimes, including an Oxford comma can create ambiguity. Consider this sentence:

The resulting solid, calcium carbonate, and powdered silica were mixed together.

It is not clear here whether two or three things were mixed together: the ‘resulting solid’ could actually be ‘calcium carbonate’ (i.e., ‘calcium carbonate’ could be a parenthetical clause).

However, these situations are relatively unusual, and they can usually be avoided by carefully phrasing the sentence in such a way that there is no scope for ambiguity.


  • The Oxford comma can usually help to avoid ambiguity, but it can very occasionally create it.
  • Most US publishers and a majority of scientific publishers worldwide use the Oxford comma.
  • Publishers’ style guides often indicate their comma preferences.
  • Whether you use Oxford commas or avoid them, ensure you are consistent throughout your document.


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