When American Airlines introduced its AAdvantage Mileage Multiplier option in May of last year, AAdvantage members could choose to purchase double or triple miles in conjunction with an eligible flight only at airport self-service check-in machines in the U.S. Now the Mileage Multiplier option can be accessed by members who select to pay a fee and earn additional miles when checking in online at AA.com or via the mobile site, mobile.aa.com. The cost of miles remains the same at approximately $.03 per mile plus a 7.5 percent sales tax, so miles are relatively expensive, but now you can deliberate and calculate whether the Mileage Multiplier is worth the extra expense when you check-in instead of having to visit a self-service check-in machine at the airport. Visit http://www.aa.com/mileagemultiplier to learn more.