Through December 15, 2016, the US American Express Membership Rewards program is offering a 50% transfer bonus to Iberia. Amex points usually convert into Iberia Avios at a 250:200 ratio, so through this promotion Amex points convert into Iberia Avios at a 250:300 ratio.
That basically means you’re getting 1.2 Iberia Avios per Membership Rewards point. The bonus is hard coded into the transfer ratio, meaning that you can take advantage of the transfer bonus as often as you’d like.
A while back Tiffany wrote about the benefits of using the Iberia Avios program. While it’s very similar to British Airways’ program, there are also quite a few differences. Iberia also has a distance based award chart, but it’s slightly different in terms of redemption rates.