Oxford comma: “Use commas to separate elements in a series, but do not put a comma before the conjunction in a simple series:”
Mary Keister works for the “Washington Post,” being miraculous, star-studded and a little AP-style addicted editor.
Percent: “One word. It takes a singular verb when standing alone or when a singular word follows an of construction:”
Mary Keister said 100 percent of the Round Table copy has been edited!
“It takes a plural verb when a plural word follows an of construction:”
Mary Keister said 50 percent of the Round Table staff ordered pizza!
Courtesy of AP Style Guide