punctuation - Using a comma before "and" in a list

I am confused as to when commas are supposed to be used before the conjunction and.

This question answers it but I am still a bit confused.

For instance the following two sentences:

• I am going to buy apples, oranges, and bananas at the store.


• I am going to buy apples, oranges and bananas at the store.

Which of the above sentences is the correct usage of a comma?

Answer

Such use of a comma is often called a "serial comma" or an "Oxford comma".

It is typically a matter of style, at least where there is no ambiguity. For example, with or without the comma, your example statement

I am going to buy apples, oranges[,] and bananas at the store.

is not ambiguous. Omission/inclusion of the comma is optional. (According to Wikipedia, use of the Oxford comma is more popular in American English than British English.)

In certain situations the serial comma can resolve some ambiguity. In these cases it should be used:

I am going to buy soup, broccoli[,] and asparagus.