The offer is:

• 7500 bonus miles for your first roundtrip
  
• 10,000 bonus miles for your second roundtrip
  
• 17,500 bonus miles for your third roundtrip

That totals 35,000 bonus miles for three roundtrips.

Flights on United and Air Canada are eligible. And most fares — but not the cheapest – are eligible (W or higher on United).

On United, MileagePlus members will earn bonus award miles on nonstop flight segments flown between the U.S. or Canada and London in fare classes F, A, J, C, D, Z, P, Y, B, M, E, U, H, Q, V and W.

On Air Canada, MileagePlus members will earn bonus award miles on nonstop flight segments flown between the U.S. or Canada and London in fare classes W, S, T, L, K, F, M, U, H, Q, V, Y, B, E, N, O, C, D, Z, P and J.

In fact, Aeroplan is offering essentially the same bonus so if you prefer to earn in your Aeroplan account you can register for their offer and credit your United or Air Canada London flights to them instead.

Registration for the United offer is required as well. Only tickets purchased starting September 15 for travel September 23 through December 12 are eligible for the MileagePlus bonus. So tickets you may have bought already prior to the launch of the promotion do not earn the bonus.

I hate it when programs punish you for not waiting for promo launches. It makes the promotion less expensive for them of course.

• it lets them only reward purchases at the margin by people who know about the promo (registration required)
  
• and purchase when they know about the promo.

But it sticks it to loyal customers who are already buying their tickets.

(HT: Frequent Flyer Bonuses)

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