When is the best time to buy an airplane ticket? As a frequent traveler, experience has taught me that the best time is mid-week. Flights always seem to be more expensive over the weekend. I like to book flights on Tuesdays.

A recent article in the Wall Street Journal supports my intuition. The Journal used the travel-booking site Kayak to check fares daily in ten markets over two weeks and found mid-week prices were the lowest. The article also quoted Harrell Associates, an airline consulting firm, which tracked 90 days of fare changes and found that prices drop mid-week.

Farecompare.com makes an even more specific claim: Tuesday at 3 PM ET is the best time to buy. They base this amazingly precise claim on three years’ worth of airline pricing data. On the other hand, Airfarewatchdog.com insists there is no special time to purchase plane tickets.

The mid-week phenomena, if it exists, might be a holdover from the days when everyone bought tickets from travel agencies and fare sales were announced in the local newspaper. Sales announced on a Friday couldn’t be acted on for several days so they were typically announced on Monday. As a result, most tickets were bought mid-week.

It’s a plausible historical explanation but wouldn’t explain why the pattern still holds. Tickets can be purchased online at any time; email and social media allow airlines to direct special offers directly to consumers. If the pattern still exists today, I doubt it will in another few years.

So what’s my advice?

Like trying to buy stocks on a dip, timing the purchase of an airline ticket is an inexact science. Instead, you are better suited to buy your ticket far enough ahead of time to get the best price. And yes, there’s a study about it: for the lowest airfare, book eight weeks in advance.