"Oxford comma" redirects here. For the song, see Oxford Comma.
In English languagepunctuation, a serial comma or series comma (also called Oxford comma and Harvard comma) is a comma placed immediately before the coordinating conjunction (usually and or or) in a series of three or more terms. For example, a list of three countries might be punctuated either as "France, Italy,and Spain" (with the serial comma), or as "France, Italyand Spain" (without the serial comma).
Its use is consistent with other means of separating items in a list (for example, when semicolons are used to separate items, a semicolon is consistently included before the last item even when and or or is present).
Its omission can suggest a stronger connection between the last two items in a series than actually exists.
Common arguments against consistent use of the serial comma:
Use of the comma is inconsistent with conventional practice.
It is redundant in a simple list because the and or the or is often meant to serve (by itself) to mark the logical separation between the final two items, unless the final two items are not truly separate items but are two parts of a compound single item.
Where space is at a premium, the comma adds unnecessary bulk to the text.
Many sources are against both systematic use and systematic avoidance of the serial comma, making recommendations in a more nuanced way (see Usage and subsequent sections).
There is ambiguity about the writer's parentage, because Ayn Rand and God can be read as in apposition to my parents, leading the reader to believe that the writer claims Ayn Rand and God are the parents. A comma before and removes the ambiguity:
To my parents, Ayn Rand, and God.
But lists can also be written in other ways that eliminate the ambiguity without introducing the serial comma, such as by changing the word order or by using other punctuation, or none, to introduce or delimit them (though the emphasis may thereby be changed):
To God, Ayn Rand and my parents.
An example collected by Nielsen Hayden was found in a newspaper account of a documentary about Merle Haggard:
Among those interviewed were his two ex-wives, Kris Kristofferson and Robert Duvall.
A serial comma following "Kris Kristofferson" would help prevent this being understood as
Among those interviewed were his two ex-wives (namely, Kris Kristofferson and Robert Duvall).
My usual breakfast is coffee, bacon and eggs and toast.
It is uncertain whether bacon and eggs, or eggs and toast, should be grouped together. Adding a serial comma removes this ambiguity. With a comma after eggs, the foods are:
Bacon and eggs
With a comma after bacon:
Eggs and toast
Writers who normally avoid the serial comma often use one in these circumstances, though sometimes re-ordering the elements of such a list can help as well.
In some circumstances using the serial comma can create ambiguity. If the widely cited book dedication above is changed to
To my mother, Ayn Rand, and God
the serial comma after Ayn Rand creates ambiguity about the writer's mother because it uses punctuation identical to that used for an appositive phrase, leaving it unclear whether this is a list of three entities (1, my mother; 2, Ayn Rand; and 3, God) or of only two entities (1, my mother, who is Ayn Rand; and 2, God). Without a serial comma, the above dedication would read: To my mother, Ayn Rand and God, a phrase ambiguous only if the reader accepts the interpretation my mother, who is both Ayn Rand and God.
The Times once published an unintentionally humorous description of a Peter Ustinov documentary, noting that "highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod and a dildo collector." This would still be ambiguous if a serial comma were added, as Mandela could then be mistaken for a demigod, although he would be precluded from being a dildo collector.
They went to Oregon with Betty, a maid, and a cook.
This is ambiguous because it is unclear whether "a maid" is an appositive describing Betty, or the second in a list of three people. On the other hand, removing the final comma:
They went to Oregon with Betty, a maid and a cook.
leaves the possibility that Betty is both a maid and a cook (with "a maid and a cook" read as a unit, in apposition to Betty). So in this case neither the serial-comma style nor the no-serial-comma style resolves the ambiguity. A writer who intends a list of three distinct people (Betty, maid, cook) may create an ambiguous sentence, regardless of whether the serial comma is adopted. Furthermore, if the reader is unaware of which convention is being used, both versions are always ambiguous.
These forms (among others) would remove the ambiguity:
They went to Oregon with Betty, who was a maid and a cook.
They went to Oregon with Betty, both a maid and a cook.
They went to Oregon with Betty, their maid and cook.
They went to Oregon with Betty (a maid) and a cook.
They went to Oregon with Betty—a maid—and a cook.
They went to Oregon with Betty, a maid, and with a cook.
They went to Oregon with the maid Betty and a cook.
They went to Oregon with a cook and Betty, a maid.
They went to Oregon with Betty, a maid; and a cook.
They went to Oregon with Betty, as well as a maid and a cook.
They went to Oregon with Betty and a maid and a cook.
They went to Oregon with Betty, one maid and a cook.
They went to Oregon with a maid, a cook, and Betty.
They went with Betty to Oregon with a maid and a cook.
The list x, y and z is unambiguous if y and z cannot be read as in apposition to x.
Equally, x, y, and z is unambiguous if y cannot be read as in apposition to x.
If neither y nor y[,] and z can be read as in apposition to x, then both forms of the list are unambiguous; but if both y and y and z can be read as in apposition to x, then both forms of the list are ambiguous.
x and y and z is unambiguous if x and y and y and z cannot both be grouped.
In her style guide Eats, Shoots & Leaves, Lynne Truss writes: "There are people who embrace the Oxford comma, and people who don't, and I'll just say this: never get between these people when drink has been taken."
In Australia, Canada, and South Africa, the serial comma tends not to be used in non-academic publications unless its absence produces ambiguity. The Australian Government Publishing Service's Style Manual for Authors, Editors and Printers (6th edition, 2002) recommends against it, except "to ensure clarity" (p. 102).
After each member within a series of three or more words, phrases, letters, or figures used with and, or, or nor.
"red, white, and blue"
"horses, mules, and cattle; but horses and mules and cattle"
"by the bolt, by the yard, or in remnants"
"a, b, and c"
"neither snow, nor rain, nor heat"
"2 days, 3 hours, and 4 minutes (series); but 70 years 11 months 6 days (age)"
Wilson Follett's Modern American Usage: A Guide (Random House, 1981), pp. 397–401
What, then, are the arguments for omitting the last comma? Only one is cogent – the saving of space. In the narrow width of a newspaper column this saving counts for more than elsewhere, which is why the omission is so nearly universal in journalism. But here or anywhere one must question whether the advantage outweighs the confusion caused by the omission ...
The recommendation here is that [writers] use the comma between all members of a series, including the last two, on the common-sense ground that to do so will preclude ambiguities and annoyances at a negligible cost
When a conjunction joins the last two elements in a series of three or more, a comma … should appear before the conjunction. Chicago strongly recommends this widely practiced usage…
"She took a photograph of her parents, the president, and the vice president."
"I want no ifs, ands, or buts."
"Their wartime rations included cabbage, turnips, and bread and butter."
In answer to a reader's query, however, The Chicago Manual of Style Online qualifies this:
... the serial comma is optional; some mainstream style guides (such as the Associated Press) don’t use it. ... there are times when using the comma (or omitting it) results in ambiguity, which is why it’s best to stay flexible.
Use a comma between elements (including before and and or) in a series of three or more items.
"the height, width, or depth"
"in a study by Stacy, Newcomb, and Bentler"
The CSE Manual for Authors, Editors, and Publishers (Council of Science Editors, 7th edition, 2006), Section 184.108.40.206
To separate the elements (words, phrases, clauses) of a simple series of more than 2 elements, including a comma before the closing “and” or “or” (the so-called serial comma). Routine use of the serial comma helps to prevent ambiguity.
Whether to include the serial comma has sparked many arguments. But it's easily answered in favor of inclusion because omitting the final comma may cause ambiguities, whereas including it never will — e.g.: “A and B, C and D, E and F[,] and G and H.”
Use commas to separate words, phrases, and clauses in a series.
AAMT Book of Style for Medical Transcription
Medical transcriptionists use the serial comma when two medications or diagnoses must be seen as separate; i.e., for "The patient was on Aspirin, Coversyl, and Dilaudid", the comma is used before "and" to avoid the reader erroneously thinking that Coversyl and Dilaudid must be taken together. 
Mainly British style guides supporting mandatory use
The Oxford Style Manual, 2002, Chapter 5, section 5.3 Comma
For a century it has been part of OUP style to retain or impose this last serial (or series) comma consistently, [...] but it is commonly used by many other publishers both here and abroad, and forms a routine part of style in US and Canadian English. [...] Given that the final comma is sometimes necessary to prevent ambiguity, it is logical to impose it uniformly, so as to obviate the need to pause and gauge each enumeration on the likelihood of its being misunderstood – especially since that likelihood is often more obvious to the reader than the writer. (pp. 121–122)
Do not put a comma before and at the end of a sequence of items unless one of the items includes another and. Thus "The doctor suggested an aspirin, half a grapefruit and a cup of broth. But he ordered scrambled eggs, whisky and soda, and a selection from the trolley."
A comma before the final "and" in lists: straightforward ones (he ate ham, eggs and chips) do not need one, but sometimes it can help the reader (he ate cereal, kippers, bacon, eggs, toast and marmalade, and tea), and sometimes it is essential:
I dedicate this book to my parents, Martin Amis, and JK Rowling
I dedicate this book to my parents, Martin Amis and JK Rowling
In British practice there's an Oxford/Cambridge divide.... In Canada and Australia the serial comma is recommended only to prevent ambiguity or misreading.
University of Oxford Public Affairs Directorate Writing and Style Guide
Note that there is generally no comma between the penultimate item and 'and'/'or' – this is sometimes referred to as the 'Oxford comma'. However, it is essential to use an Oxford comma if required to prevent ambiguity:
He took French, Spanish, and Maths A-levels.
I ate fish and chips, bread and jam, and ice cream. (icons as original)
Mainly American style guides opposing mandatory use
Use commas to separate elements in a series, but do not put a comma before the conjunction in a simple series: The flag is red, white and blue. He would nominate Tom, Dick or Harry.
Put a comma before the concluding conjunction in a series, however, if an integral element of the series requires a conjunction: I had orange juice, toast, and ham and eggs for breakfast.
Use a comma also before the concluding conjunction in a complex series of phrases: The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude.
In the United States, the choice is between journalistic style (no serial comma) and "literary" style (with serial comma); consistent use of the serial comma is usually recommended for college writing.
Australian style guides opposing mandatory use
A comma is used before and, or, or etc. in a list when its omission might either give rise to ambiguity or cause the last word or phrase to be construed with a preposition in the preceding phrase: "There were many expeditions, including those of Sturt, Mitchell, Burke and Wills, and Darling." "The long days at work, the nights of intense study, and inadequate food eventually caused them serious health problems." "The sea, the perfume of wisteria, or a summer lunch: any of these revived memories of an easier time." "We needed to know how to get there, what time to get there, the number of participants, etc."
Generally, however, a comma is not used before and, or or etc. in a list: "John, Warren and Peter came to dinner." "Fruit, vegetables or cereals may be substituted." "Why not hire your skis, boots, overpants etc.?"
As of December 2015[update], the manual of style guide for writers of Wikipedia articles permits use of either convention but recommends consistency within each article, while stating that either convention can create or remove ambiguity.
^Sometimes, the term also denotes the comma that might come before etc. at the end of a list (see the Australian Government Publishing Service's Style Manual for Authors, Editors, and Printers, below). Such an extension is reasonable, since etc. is the abbreviation of the Latin phrase et cetera (lit. and other things).
^The serial comma sometimes refers to any of the separator commas in a list, but this is a rare, old-fashioned usage. Herein, the term is used only as defined above.
^ abcdStrunk, Jr., William; White, E. B. (2005). The Elements of Style. Illustrated by Maira Kalman (Illustrated ed.). Penguin Press. p. 3. ISBN9781594200694. Retrieved February 15, 2013. In a series of three or more terms with a single conjunction, use a comma after each term except the last.
^Truss, Lynn (2004). Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation. New York: Gotham Books. p. 84. ISBN1-59240-087-6.
^The Oxford Style Manual, 2002: "The presence or lack of a comma before and or or ... has become the subject of much spirited debate. For a century it has been part of OUP style ..., to the extent that the convention has come to be called the 'Oxford comma'. But it is commonly used by many other publishers here and abroad, and forms a routine part of style in US and Canadian English" (p. 121).
^McArthur, Tom, "Comma." Concise Oxford Companion to the English Language. 1998. Encyclopedia.com.
^Garner, Bryan A. (2009). Garner's Modern American Usage (3rd ed.). Oxford University Press. p. 676. ISBN978-0-19-538275-4. ... omitting the final comma may cause ambiguities, whereas including it never will ...
^The Oxford Style Manual, 2002: "But it is commonly used by many other publishers here and abroad, and forms a routine part of style in US and Canadian English" (p. 121).
^The Oxford Style Manual, 2002; from discussion of the serial comma: "If the last item in a list has emphasis equal to the previous ones, it needs a comma to create a pause of equal weight to those that came before" (p. 121). The University of Oxford itself is quite distinct from Oxford University Press, and gives different advice. See University of Oxford Writing and Style Guide, below in this article.
^The Oxford Style Manual, 2002; from discussion of the serial comma: "The last comma serves also to resolve ambiguity, particularly when any of the items are compound terms joined by a conjunction" (p. 122).
^The Oxford Style Manual, 2002; in discussion of the semicolon, examples are given in which complex listed items are separated by semicolons, with the same structure and on the same principles as are consistently recommended for use of the comma as a list separator in the preceding section (pp. 124–5)
^"Rhetorical Grammar: Grammatical Choices, Rhetorical Effects. 4th Ed.", 2003; This punctuation style, however, does have a drawback: It may imply a closer connection than actually exists between the last two elements of the series (p. 89)
^Ridout, R., and Witting, C., The Facts of English, Pan, 1973, p. 79: "Usually in such lists 'and' is not preceded by a comma, [...]".
^Implicit in the treatment given in The Australian Government Publishing Service's Style Manual for Authors, Editors and Printers, 6th edition, Wiley, 2002, on p. 102. The exception discussed (see Usage, below) makes sense only on the assumption of this argument.
^Nielsen Hayden, Teresa (1994). Making Book. Framingham, Massachusetts: The NESFA Press. p. 143.
^"Making Light". Nielsenhayden.com. October 21, 2010. Retrieved February 10, 2013.
^Norris, Mary (2015). Between You & Me: Confessions of a Comma Queen. W. W. Norton. Chapter 5. ISBN978-0-393-24660-5.
^Perlman, Merrill (March 6, 2007). "Talk to the Newsroom: Director of Copy Desks Merrill Perlman". The New York Times.
^Norman Goldstein, ed. (2002). The Associated Press Stylebook and Briefing on Media Law. Cambridge, Massachusetts: Perseus. pp. 329–330. ISBN0-7382-0740-3.
^Gramlich, Andy (2005). "Commas: the biggest little quirks in the English language"(pdf). Hohonu3 (3): 71. Retrieved 17 December 2013. It's just a matter of STYLE, and in this case, newspaper or literary (book) style. . . . Choose one style or the other the authorities say, but be consistent. Most writers recommend the literary style in college writing to avoid possible confusion . . .
^Grevisse, Maurice (1988). "Ponctuation: la virgule dans la coordination". Le bon usage: grammaire française (in French). Revised by André Goosse (12th ed.). Paris-Gembloux: Duculot. pp. §124 (c) Remarque 1. ISBN2-8011-0588-0.