From Wikipedia: "Opinions vary among writers and editors on the usage or avoidance of the serial comma. In American English, the serial comma is standard usage

From Wikipedia: "Opinions vary among writers and editors on the usage or avoidance of the serial comma. In American English, the serial comma is standard usage in non-journalistic writing that follows the Chicago Manual of Style. Journalists, however, usually follow the AP Stylebook, which advises against it." http://en.wikipedia.org/wiki/Serial_comma http://en.wikipedia.org/wiki/Serial_comma