Backstreet Boys' Jive album "Millennium" is the best-selling album so far this year, according to mid-year certification figures from the Recording Industry Association of America (RIAA). Six weeks after its release, the Boys' second U.S. album is already certified at the five million mark, which puts it halfway to matching the total sales-to-date of the group's eponymous debut set.

Backstreet Boys are only one of the youth-oriented pop acts that dominated sales in the first half of the year. Ricky Martin's self-titled C2/Columbia set and Britney Spears' " ... Baby One More Time" (Jive), both released in the past six months, have hit the four-million plateau, while 'N Sync's eponymous RCA set has moved three million more copies this year, pushing its grand total to seven million.

2Pac's double set, "Greatest Hits" (Amaru/Death Row/Interscope), is the midyear's top hardcore rap album, certified at five million, while TLC's LaFace/Arista set "Fanmail" has delivered four million in sales so far this year, making it the top hip-hop collection.

Top rock albums at midyear are Metallica's double set, "Garbage Inc." (Elektra/EEG), which hits the four million mark, and the Offspring's Columbia album "Americana," which has moved three million units in the past six months, pushing its certified total to four million.

As for June certification highlights, Shania Twain's "Come On Over" (Mercury Nashville) hit the 11 million mark, and Dixie Chicks' "Wide Open Spaces" (Columbia Nashville) hit six million.

-- Chris Morris, L.A.