Is there some magical day of the week to purchase airfare? Unlike the advanced-booking question, this one has a more definitive answer: Tuesday (and sometimes Wednesday). Most airlines release sales early in the week, often on Mondays, which leaves other airlines scrambling to match prices. By Tuesday afternoon, most competing airlines have engaged in an all-out fare war. These sales usually last through Thursday, but since they tend to have very limited availability, you want to check fares on Tuesday (early Wednesday at the latest), and book immediately.