The Oxford comma

Also called a serial or Harvard comma, the Oxford comma goes before the final conjunction ("and" or "or") in a series. It is always correct to use it, but it's not always necessary. Schools teach to always omit the Oxford comma, but that's definitely wrong: there are times when you must use it to prevent misreading or ambiguity. Consider these examples:

The colours available are black, white, yellow, and red.

In this case, you could omit the final comma before the “and”, but you don't have to.

Resources are available for policy development, drafting the consequential procedures, and consultations with the minister's office and other stakeholders.

The Oxford comma is needed because it prevents reading through into the final phrase. That is, without the comma, the reader might read the second phrase as “...drafting the consequential procedures and consultations...”

Provision has been made for site rehabilitation, occupational health and safety, and any continuing costs.

The Oxford comma is needed because the second phrase contains the conjunction "and". If you remove the final comma, the phrasing gets a bit confused.

Using the Oxford comma is one of the marks of a professional writer, but it’s a good habit for everyone to develop, even when it isn’t strictly needed.

For more information, see Punctuation>Comma in the Doxical Style Guide for Miners and Geoscientists.