The least expensive day of the week to fly is Tuesday. The most expensive day to fly is Sunday, followed closely by Friday. For my business travels I do not have a choice what day of the week to fly - I can only hope my schedule permits me to fly on a Tuesday (or a Wednesday) and NOT on a Sunday. When I book my Jamaica trips I try to book for Tuesdays as well - even using FF miles we have a better shot of getting that mileage seat on that day of the week as opposed to a Sunday.