Which is correct?
I’m going to need eggs, flour, butter, and chocolate chips for the cookies.
I’m going to need eggs, flour, butter and chocolate chips for the cookies.
Yes, the correct punctuation is the oxford comma in the first sentence.
The oxford comma comes before the “and” in a list of things.
Also known as the “serial comma,” the Oxford comma is the sometimes-optional final comma in a list of things. For example, the comma after “milk” in the below sentence:
Gordon bought bread, milk, and eggs at the grocery store.
Some style guides insist on the Oxford comma, and others think it’s no big deal. But, neglecting to use it can lead to some serious misunderstandings.
I’m having breakfast with my parents, Beyonce and Jay-Z.
The lack of an Oxford comma in this sentence makes its meaning ambiguous. Is the speaker having breakfast with four people — Mom, Dad, Beyonce, and Jay-Z? Or are their parents actually Beyonce and Jay-Z? Inquiring minds want to know. A final comma in the series would clear up the confusion.
6.19: Serial commas
Items in a series are normally separated by commas (but see 6.60). When a conjunction joins the last two elements in a series of three or more, a comma—known as the serial or series comma or the Oxford comma—should appear before the conjunction. Chicago strongly recommends this widely practiced usage, blessed by Fowler and other authorities (see bibliog. 1.2), since it prevents ambiguity. If the last element consists of a pair joined by and, the pair should still be preceded by a serial comma and the first and (as in the last two examples below). (CMOS)