Links in this essay will take you to information about the usage experts and their work. Numbers in parentheses are page references in the sources.
Commas with items in a series
Usage varies on the matter of the serial comma (or Oxford comma)—the comma between the last two items in a series of words, phrases, or clauses. Newspapers routinely omit that last comma, and book editors just as routinely put it in. Does this mean that the comma is merely a matter of taste? Usage experts don't think so.
Yes, newspapers ask journalists to omit the comma to save space—or even ink—and journalists wisely comply. Even so, most experts agree that the practice itself may not be so wise, because omitting the comma can result in ambiguity or misreading. Wilson Follett gives an example of ambiguity:
In the following year he will specialize in gynecology, immunology, orthopedics or diseases of the bone.
How many items are in the series—three or four? We can't be sure. In fact, the writer meant to list four items, says Follett, and the comma would have made this clear (399).
Omitting the comma can also cause misreading, as in this next example, fromRoy Copperud:
They had brown, green, gray and blue eyes.
Copperud explains that "gray eyes and blue eyes is meant, but gray-and-blue eyes is what may be understood without the comma [after gray]" (94).
Follett concludes that "omission [of the comma] always tends to confusion and sometimes guarantees it; inclusion can never possibly confuse" (399). And Bryan Garner concurs: "Omitting the final comma may cause ambiguities, whereas including it never will" (676).
So if you are writing for a publisher who asks that you omit the comma, by all means do so. Otherwise, use that comma—it is worth both the space and the ink.
Source: Hacker Handbooks (Boston: Bedford, 2013).