Gary Steiger has done a good job of outlining how to earn miles more or less for free by purchasing savings bonds online with a points earning credit card. You can transfer the balance to a no interest special offer card, too — thereby earning the miles and the interest at no cost.

You can buy up to $60,000 worth of bonds this way. If you use a double miles earning credit card (such as the Delta Amex which offers double miles through July 15) you can earn 120,000 miles for free.

That’s enough for a first class ticket to Australia or two coach tickets to Australia or 5000 miles short of five domestic coach tickets.

Click on the link above and choose finance from his menu on the left hand column of the page.

Update: Gary Steiger emails the following:

Alas, the Delta double miles offer is for 20000 bonus miles max. As I see it, currently you can buy $20000 of bonds for 40000 miles, and $40000 of bonds on a Starwoods Amex for 50000 miles, for a total of 90000 miles. But maybe someone else will come along with a double miles offer before the end of the year (when the whole buying by credit card deal goes away).