NEW YORK (Billboard) - Two of country music's biggest stars are joining forces for a U.S. tour early next year.

Keith Urban and Carrie Underwood will hit the road together beginning January 31 in a city to be announced. The outing will play 24 dates to be announced; tickets go on sale December 1.

First, Urban will cap a hard-touring 2007 with North American dates through mid-December. On Tuesday, he will release the compilation "Greatest Hits: 18 Kids."

Underwood will be touring in support of her second album, "Carnival Ride," which recently debuted at No. 1 on The Billboard 200.

Here are the cities for the Urban/Underwood tour: Uncasville, Conn.; New York; Atlantic City, N.J.; Tallahassee, Fla.; Biloxi, Miss.; Kansas City, Mo.; Omaha, Neb.; San Jose, Calif.; Baltimore; State College, Pa.; Charlotte, N.C.; Gwinnett, Ga.; Rochester, N.Y.; Hershey, Pa.; Roanoke, Va.; Charleston, W.Va.; Bossier City, La.; Wichita, Kan.; Denver, Anaheim, Calif.; Charlottesville, Va.; N. Charleston, S.C.; Raleigh, N.Y.; Lexington, Ky.