No, they are not. But they would like to fill up the seats on the less popular days. Otherwise those seats are a total loss for them. Which is why you will find the best deals are available for flights on Tuesdays, Wednesdays and Saturdays. Now, when it comes to the days everyone wants to fly -- Fridays and Sundays -- it figures that those are almost always the most expensive days to fly. Adjust your vacation schedule accordingly.