PHILADELPHIA (AFP) - American world champions Allyson Felix, Tyson Gay, Jeremy Wariner and Lauryn Williams continue their preparations for the Beijing Olympics by competing at Saturday's Penn Relays.

The USA versus World format will help athletes and coaches see where they stand in the Olympic pecking order with just 104 days to go before the Summer Games.

The Penn Relays at Franklin Field is part of a six-race series of relays.

Against close to 150 athletes from 11 countries, the Americans will have the opportunity to impress selectors in Team USA colors, knowing that if they are successful as individuals at the Olympic Team Track and Field trials in Eugene, Oregon from June 27-July 6, they will be at the front of the line for relay team selection.