Commas in Lists of Items
According to The Elements of Style and The Chicago Manuel of Style, when listing three items, a comma is placed after the first and second items (Paper, pen, and writer). Some publishers omit the second comma, but they won’t fault you for not knowing their style. The important thing is to be consistent, so the editor can match the style sheet to your manuscript. Plus, if the list contains multiple words, it can be confusing if you don’t add the second comma. (His pets consisted of a long-haired cat, a short-haired dog, and a very noisy parrot.)
The exception to this rule concerns the name of businesses such as law firms which usually omit the last comma (Dewey, Sokum and Howe).
To further complicate things, if the list of items includes commas, they should be set off by semi-colons (The blank, white sheet of paper; the black, fine-line pen; and the ready, spirit-filled writer).