Individually, sisters Shelby Lynne and Allison Moorer are two of country and Americana music's most highly-regarded vocalists. In 2010, their Side-by-Side tour gave many fans their first taste of the familial harmony they have shared but never harnessed on record -- until now. The pair have revealed that they are currently working on their first album together, which they expect to release in 2012.

"We're starting to write in March and hopefully we'll put out a record next year," Shelby tells Billboard. "We're going into uncharted territory here. We'll see what happens. I expect it to be really good and really soulful. We're just a couple of singers who happen to be sisters ... getting together to write songs and see what we can do together."

Shelby -- who lives in California, while Allison and her husband, musician Steve Earle, are based in New York City -- cites the success of the tour and the opportunity it afforded the sisters to grow even closer as the impetus for the upcoming project.

"It was just the two of us on two guitars," she says. "Having not written anything yet we did each other's songs and reached back into our childhood and grabbed a couple of things that we grew up singing. It worked brilliantly. We both like to tell stories and cut up and have fun and go with the flow ... we don't fight. I know everybody would love that to be the case, but that's not the way it is, and I don't see anything like that happening."

On a tour stop at the legendary Birchmere in Alexandria, Va., last year, the pair performed a song titled 'Where You Are,' which seems a natural fit for this collaborative project, as Allison told Shelby during the show, "I wrote that song years ago for the two of us. When it didn't work out, I ended up singing both parts ... I'm so happy I finally get to sing it with you."

Although they endured turbulent times as youngsters, family harmony was definitely a part of the sisters' upbringing.

'Without a doubt we grew up listening to the Everly Brothers and Elvis Presley and pop music from the '30s and '40s era," Shelby told The Boot just prior to the launch of the tour last year. "That's where we learned harmonies. Singing together, it's the old familiar uniform that feels so natural. We have never done anything else as well as sing together. Sometimes I have to pinch myself and say, 'Are we really doing this?'"

In 2010, Shelby released two albums, 'Tears, Lies and Alibis,' and 'Merry Christmas,' both on her own Everso Records label. Allison released her latest album, 'Crows,' in February and gave birth to her son, John Henry, in April.