It's no secret that movie soundtrack albums have suffered a significant sales slump in the last several years. But soundtracks of animated films have fared particularly poorly.

The Rhino soundtrack to "Alvin and the Chipmunks: The Squeakquel" was the biggest-selling soundtrack for an animated feature in both 2009 and 2010, selling 274,000 and 451,000 units in the United States, respectively, according to Nielsen SoundScan.

But aside from Alvin, Theodore and Simon's cinematic success, only one other animated film in the last two years has spawned a soundtrack album with sales topping 100,000: Disney's "The Princess and the Frog," which has sold 154,000 units to date, according to SoundScan.

Consider the slippage in DreamWorks' "Shrek" franchise. The first film, released in 2001, did $267.7 million at the box office, according to Box Office Mojo, and sold 2.5 million copies of its soundtrack, according to SoundScan. "Shrek 2," the highest-grossing animated feature in history at $441.2 million, generated soundtrack sales of 1.2 million. "Shrek the Third," released in 2007, tallied $322.7 million in movie ticket sales but a mere 114,000 units in soundtrack sales. And last year's digital-only soundtrack to "Shrek Forever After," which grossed $238.7 million, sold only 9,000 units.

Interscope's soundtrack to "Rio" is hitting retail just as Disney Records is releasing the soundtrack to the tween-targeted film "Prom" and the Disney Channel TV movie "Lemonade Mouth."

"Tweens move so quickly now, getting so much information virally," Walt Disney Records VP of marketing Rob Souriall says. "You used to have to beat kids over the head with a message for nine months and now that's too long. The new strategies are shorter windows and more focused."

Singles have become an even tougher sell, especially when an animated film targets a preteen audience. The playlist at Radio Disney, for example, is generally a 50/50 split between Disney-related artists and standard top 40 songs, station group GM Sean Cocchia says.

"Animated films, for the most part, have songs that are much more in a Broadway style," he says. "We're more about contemporary music than show tunes."

Soundtracks of recent animated movies, even those that find a large audience, have posted weak sales. The soundtrack albums for last year's box-office hits "How to Train Your Dragon" and "Despicable Me" have sold just 30,000 and 25,000, respectively, according to SoundScan.

The last major non-Disney hit soundtrack came 15 years ago when "Space Jam" delivered a slam-dunk for the music business, selling 4.8 million units of a soundtrack that included R. Kelly's "I Believe I Can Fly."

"The soundtrack retail picture is a challenge," says Anthony Seyler, VP of film and TV marketing and soundtracks at Interscope Geffen A&M. "But when a film has great legs, we have a chance."