Northwest continues to please by offering bonus miles for next to nothing. Check out their latest Refer-A-Friend promotion, where you can earn up to 20,000 miles for your friends’ travel when you refer them to Northwest WorldPerks. You can earn up to 4,000 miles for each of five friends, and your friends can earn an unlimited number of bonus miles.

Registration is required before May 15. Upon registering, you’ll receive a confirmation email that you can send to up to five friends. To be eligible, your friends must sign up to be WorldPerks members (or join the program prior to receiving your email) and may not have earned Northwest miles for travel since Jan. 1, 2005. Your friends then have until May 31 to complete specific activities, like purchasing a ticket at nwa.com (500 miles) or checking in online (500 miles).

Visit http://www.nwa.com/offers/referafriend/ for details.