While inspecting my CD collection one day, the Better Half innocently asked me why some CDs were credited to Tom Petty and some were credited to Tom Petty & The Heartbreakers.

Considering that Petty often uses the band’s members in his “solo” albums, it wasn’t an easy answer. I’m sure it comes down to the level of collaboration involved in the songs, but, to the listener, there isn’t really an easily discernible difference; Petty’s unique songwriting gift is the dominant force, no matter who gets the credit.

Well, Tom seems like he wants to change that on Mojo, the band’s new release, as he allows the Heartbreakers to cut loose with abandon. In particular, he gives longtime right-hand man Mike Campbell the opportunity to show off his chops on lead guitar. Campbell has always been subservient to the songs in the past, but this album is as much his showcase as it is Petty’s.

While that may do wonders for Campbell’s status as a guitar hero, I’m not sure that it does that much for this album’s standing amongst the band’s formidable catalog. The solos are fine, but they are often the high points of so-so material that falls below the memorable work that Petty has uniformly done in his 30-plus years in the business.

When Petty and the boys played on Saturday Night Live in May to preview the new release, they played with ferocity and fire that made them sound like hungry up-and-comers rather than esteemed rock royalty. It turns out that was because of a well-chosen set list.

The two songs they played that night, “Jefferson Jericho Blues” and “I Should Have Known It,” are the two most energetic on the new disc. The latter is especially fierce, with Campbell channeling Jimmy Page in a monster riff while Petty snarls appropriately about a wayward lover.

Had Mojo followed that vein, things could have been more promising. But, as any regular listener of his Buried Treasure radio show knows, Petty has a serious love for the blues, and he indulges this love time and again on the album. Whether mimicking Muddy Waters (“Takin’ My Time”) or the Stones take on Muddy Waters (“U.S. 41”), these songs, and several other bluesy numbers, never come off as more than well-done homages.

The characters within run the gamut from ribald to woebegone but are little more than genre stereotypes, making it awfully hard to connect with or care about them.

Elsewhere, the Heartbreakers are given the chance to jam on several songs featuring extended running times. With Petty’s vocals merely sparse interruptions among the drawn-out instrumental work, the band grinds along on the Grateful Dead space-rock of “First Flash Of Freedom,” the slightly funky “Running Man’s Bible,” or the vaguely reggaefied immigrant’s lament “Don’t Pull Me Over,” but they don’t ever really set the songs alight.

Only the spooky groove on “The Trip To Pirate’s Grove,” featuring Benmont Tench’s Doors-inspired keyboard tinkling, really connects out of all the longer songs.

Just when it seems like Mojo is running completely off course, Petty pulls it together for the final two tracks, stunners that remind everyone that this band is still inspired enough to produce more than just echoes of past glories.

On “Something Good Coming,” Campbell goes back to playing around the edges of this wistful ballad, while Petty lives deep within the hard-luck character, making the song’s title seem more like a threat than a promise.

The dark, spiraling “Good Enough” follows up with Abbey Road-style moody majesty, the band putting in its finest effort by far. Petty responds in kind with his signature mix of wit and wisdom on the lyrics: “God bless this land, God bless this whiskey/I can’t trust love, it’s far too risky.”

The protagonist here knows that good enough is really all he can ever achieve in life; luckily, the thundering musical outro lets out all of his pent-up frustrations.

If Petty is intent on showing off his band as more than just extensions of his own talent, then he should make sure to give them songs like those last two to strut their stuff.

After listening to Mojo, I realized how much the Heartbreakers do bring to the table as opposed to the solo albums, even if the difference is subtle. What they do best is give an extra burst of reckless energy to Petty’s inward-looking characters, the fire in their bellies that’s at odds with the torment in their souls.

That’s a far more difficult magic to capture than the rote bluesy jamming they’re asked to perform over the bulk of Mojo, which, ironically enough, finds them, and Petty, save for a few outstanding exceptions, disdaining the true mojo that makes them so special.

SAMPLE PETTY'S "MOJO"

Adobe Flash Required for flash player."I Should Have Known It"

Adobe Flash Required for flash player."Something Good Coming"

Adobe Flash Required for flash player."Good Enough"