They'll open the eight-day meet in Omaha, Neb., on Monday in the 400-meter individual medley, a grueling event that Phelps had said he wasn't going to swim anymore after the 2008 Olympics, where he won a record eight gold medals. He holds the world record in the event.
Their other events against each other will be the 100 and 200 freestyle, 200 backstroke, 200 IM and 100 butterfly. Phelps is entered in the 200 butterfly; Lochte is set to swim the 100 back.
Phelps' other world records are in the 100 and 200 butterfly. He holds the American record in the 200 free.
Lochte's lone world record is in the 200 IM from last year's world championships, the first world mark set since high-tech bodysuits were banned.
On the women's side, 17-year-old Missy Franklin is entered in five events: 50 free, 100 and 200 backstroke, and 100 and 200 freestyle.