DH and I received a 25% bonus miles offer from Amex Delta skymiles. I called before I enrolled to be sure that I wasn't eliminating an ongoing double miles offer. I wasn't, mine was done Sept. 30. DH however has an ongoing triple miles offer until the end of October. The representative said that enrolling in the 25% mileage bonus would not affect that offer. I checked on flyertalk however and other posters are not able to get the larger mileage promotions by enrolling in the smaller one. You may want to wait to see if you are going to get a better double miles offer before enrolling in the 25% bonus. If I run into a problem, I will just start using my business Delta Skymiles card again. In fact, I think when I don't use it, I get promotions.