LOS ANGELES—Kobalt Music Group Ltd., an upstart music publisher that is now one of the world's biggest, said Tuesday that it will manage the copyrights of Paul McCartney's post-Beatles songs such as "Ebony and Ivory" and "Band on the Run" along with works managed by McCartney's MPL Communications group outside of North America and the U.K.

The deal marks a break for McCartney from EMI, which was acquired for $2.2 billion by a group of investors led by Sony/ATV last month, making it the world's biggest music publisher.

The move ensures different managers for McCartney's Beatles and non-Beatles hits in markets not already served by MPL.

It also represents the growing popularity of Kobalt among artists.

According to Billboard magazine, Kobalt increased its share of publishing revenue from the top 100 U.S. radio hits to 15.5 percent in the third quarter of 2011, up from less than 5 percent three years earlier. That ranked it second behind only EMI, which had 17.9 percent at the time.

Kobalt says it pays songwriters about 25 percent more than other publishers because of its streamlined structure and better tracking of song plays around the world.

"We have grown by delivering service, quality, and results to our clients. We have not bought our growth. We have earned it," said Kobalt CEO and founder Willard Ahdritz in an interview.