When best to book airline tickets

The weekends are the worst time to make reservations because fares tend to be the highest. As you see from the chart, midweek is a lot better, preferably Tuesday. That's because sales are often launched Monday night. From the WSJ's Scott McCartney:

When airlines want to push through a fare increase, marking up their basic prices across the board usually by $5 or $10, they often do that on Thursday night, then watch to see if competitors match and if the higher rates stick over the weekend. If competitors balk, prices can be rolled back by Monday morning. In addition, airlines don't manage their inventory as actively on weekends, so if cheap seats sell on some flights, prices automatically jump higher. Fare analysts may decide later to offer more seats at cheaper prices, but not until they come back to work on Monday, according to airline pricing executives.

That's why a ticket can be $199 on certain days and $499 on other days, even when booking months in advance.