One of Chase’s more popular cards is the Chase United MileagePlus Card, the standard bonus on this card is 30,000 Miles (plus 5,000 for adding an authorized user), but it’s frequently possible to get 50,000 miles. There are currently two ways of getting this offer:

Chase Branch
I haven’t verified that this offer is available at all Chase branches, but it has been available at 100% of the places I have been able to get checked. You should find the promotional flyer in branch, if not just ask for it. Please share your experiences in the comments.
United Shopping Portal
PointsCentric shared that he received this 50,000 mile offer after making a purchase through the United shopping portal, since then he’s had multiple other people try it. Not everybody has had success, but the majority of people have. People have generally received a targeted mailer a few weeks after their portal purchase. The United shopping portal has iTunes, so you should be able to purchase a cheap song from there to trigger the offer.
Our Verdict
55,000 miles isn’t the best ever offer on this card (that was 55k miles + $50 statement credit in April of this year), but it is one of the better offers around. If you have plans that involve United and need some additional miles, this is a pretty good offer otherwise I’d just wait and try to snag a 55k + $50 offer (if they bring that back). It’s also still possible to get the 50,000 mile offer on the business version of this card.
