It may sound like a mixed metaphor. The three eclectic singers of Tenors Unlimited were inspired by the Three Tenors, the popular singing group in the 1990s and 2000s consisting of classical opera singers Jose Carreras, Placido Domingo and Luciano Pavarotti.

But the Tenors Unlimited — Scott Ciscon, Paul Martin and Jem Sharples – have a nickname that suggests a very different image. Aka The Rat Pack of Opera, the association is with the original Rat Packers — Frank Sinatra, Dean Martin and Sammy Davis Jr. Both groups engage in banter, but the vocals are far more important than the light-hearted quips. For the Tenors Unlimited, it’s not about the wild lifestyle of the Las Vegas Rat Packers, but about their charisma, talent and camaraderie.

The trio’s repertoire does include classical opera, but also pop and crooner classics and their own original compositions. They have shared the stage with such stars as Beyoncé, Sting and Lionel Ritchie, as well as the London-based Royal Philharmonic Orchestra.

After solid solo careers, according to Sharples, they came together fortuitously. “We met nearly 17 years ago and have been working together for 15 years,” he said. “At the time, there was nothing like that in our genre.” Now the three have embarked on a 15th anniversary tour through the United States and the United Kingdom, with Germantown’s BlackRock Center for the Arts their March 16 stop.

The original Three Tenors probably had more in common in terms of musical training, being all European and from the classical opera stage.

Chicago-born Ciscon studied engineering and communications in college while “singing from birth,” he said. A Broadway audition took him to Germany and later London’s West End, where he appeared in a number of musicals.

Paul Martin first sang in a local church choir and joined the National Youth Choir of Great Britain. Trained in opera, he embarked on a career in the art form — performing with opera companies and ensembles all over Europe, Japan and the U.S. While he was singing in a production of Puccini’s “Turandot” in the Netherlands, he heard Tenors Unlimited were looking for a third member.

“I was a freelance singer with the Dutch National Opera until a friend told me my job was ‘being advertised,'” Martin recalled.

Sharples, who also is British, took private lessons and trained at the Guildhall School of Music and Drama. His career started in musicals. Having appeared on TV as well, he co-wrote, produced and played the lead in a new musical called “Nelson,” based on the life and loves of British naval hero Horatio Nelson.

The three voices of Tenors Unlimited are not all tenors. “I’m the bass-baritone of the group,” “I supply the lower harmonies,” said Martin. “[It can] get so dull with only one type of voice. This gives us richer color.”

As does the inclusion of solos as well as group numbers, said Sharples. “We can sing to service the tune, and not just do thee-part harmony.”

Even the two tenors of the trio are not sound-alikes: Sharples is more classical, and Ciscon is more of a “popular” tenor. “We’re not competing for the same note,” said Martin. “We have vocal space.”

Martin was drawn to the opportunity to write music with the group and also “not to be restricted to one opera or one part, but to be able to sing as myself.” Ciscon, who acts as the group’s spokesman, agreed to the appeal of “singing as me” rather than in a role.

During their anniversary tour, the singers are performing their own favorite pieces and those that have been most popular among audiences. They range from classic opera, such as the bravura aria “Nessun Dorma” from Puccini’s “Tosca” to crossover, of the type represented by tenor Andrea Bocelli, in a mix of voices, styles and personalities. “It’s a show, not just a concert,” Ciscon said.

This may be audience members’ first time to hear the iconic song “The Impossible Dream” (from “Man of La Mancha”) with three voices instead of one. Also on the program are the “Toreador” song from Bizet’s opera “Carmen,” a few “Les Misérables” tunes and crooner numbers like “Everything” (Michael Bublé) and “Can’t Take My Eyes Off You” (Franki Valli). There may even be a Freddie Mercury song.

Pianist Gary Adler, who wrote the musical “Altar Boyz,” will accompany the performance.

“Their voices are exquisite,” said Alyona Ushe, BlackRock’s executive director. “We’re honored to have such a celebrated trio coming to our venue.”

Tenors Unlimited expresses it differently. “Come along to the concert,” Ciscon said. “You’ll find it light-hearted with great singing and harmonies. People have told us they weren’t sure about the show — because people tend to go to what they know — but they found the show uplifting.”

The three have more or less given up on their solo careers, although Martin directs a local choir, and Sharples gives private voice lessons. “We found that the whole is greater than the sum of its parts,” Ciscon said. “Tenors Unlimited really pays off.”

Tenors Unlimited will perform at 8 p.m. Saturday, March 16, at BlackRock Center for the Arts, 12901 Town Commons Drive, Germantown. Tickets range from $25 to $45. Call 301-528-0180 or visit www.blackrockcenter.org.