The Oxford comma is known by several names, such as serial comma or Harvard comma, and is the comma that goes just before a conjunction in a list. If you’d like to get a flavor for the controversy over its use, see the Wikipedia entry on the serial comma. People do get quite passionate about such little things!
For years I always thought of the first example as correct, and perhaps you have too. It’s economical, after all, and since every comma inserts a bit of a break in the way a sentence is read (even when you’re just reading silently to yourself), the second sentence takes longer.
But the trend is in the direction of the comma prior to the conjunction. The Chicago Manual of Style, an influential guidebook, devotes more than ten pages to commas. But, even in my 1982 edition, Rule 5.50 says, “When a conjunction joins the last two elements in a series, a comma is used before the conjunction.” The Manual gives an example: “We have a choice of copper, silver, or gold.”
The Webster’s Dictionary of English Usage (1989) is not so clear. It states, “There is also a good deal of comment on the use or nonuse of a comma before the coordinating conjunction in a series of three or more. In spite of all the discussion, practice boils down to the writer’s personal preference, or sometimes a house or organizational style. Additional comment is not needed.”
In other words, do what you want.
And I did for years. But what made me think about it again was Book 7 of the Harry Potter series. The books uses the comma prior to the conjunction in every case. This made me think about the issue, but was not quite compelling. But what settled it for me was, of all things, the Microsoft Manual of Style for Technical Publications, which I stumbled across on Amazon and purchased. Page 173 is quite explicit: “When a conjunction joins the last two elements in a series, use a comma before the conjunction.”
But what I find compelling is the reason the Microsoft Manual urges such rigidity. Much technical literature is machine-translated and not proofread prior to release. Microsoft releases a flood of technical information every year in many languages. Employing language specialists is much too costly (plus they’re hard to find). So the Oxford comma is placed in text for a simple reason: clarity. And that provided an answer for the Harry Potter books, which are translated into dozens of languages. I suspect the Harry Potter translation is first done by a computer, then reviewed by a language specialist.
That got me to thinking. I like clean, clear writing. I review every sentence to ensure it has only the intended meaning. And that pesky Oxford comma helps provide clarity.
That’s good enough for me. I suggest you do likewise.