Although “blessed” by Fowler and the Chicago Manual of Style, the serial comma is readily dropped by a growing number of writers who prefer the advice given in the AP Style Guide:
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.
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 egg for breakfast.
In the Penguin Guide to Punctuation, R.L Trask likewise recommends omitting a comma before and. As does the AP guide, he says the only excuse for placing a comma before the and is to avoid ambiguity.
Trask points out another use of what he calls the “listing comma.”
In a list of adjectives all describing the same noun, a comma may be used to separate them: My dog’s long, dense, rough fur requires frequent brushing.
A frequent error is to place commas between adjectives that are not all describing the same noun: My first pet was a purebred, Alaskan Husky.
By remembering that the listing comma is a substitute for the word and, writers can avoid error by mentally replacing each comma in a list of adjectives with the word and.
Compare the following examples:
My dog’s long and dense and rough fur needs frequent brushing.
My first pet was a purebred and Alaskan Husky
In the first example, replacing the commas with the word and makes the expression cumbersome, but it does not alter the sense. All three adjectives describe the same noun, “fur.”
In the second example, replacing the comma with and makes no sense because “purebred” does not describe “Husky”; it describes “Alaskan Husky.” It’s sufficient to write, “My first pet was a purebred Alaskan Husky.”