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After Petra's retirement, Hartman started working with former Petra singer, John Schlitt, as II Guys from Petra in an album which was released in January 26, 2007 titled Vertical Expressions.
The reprise features an all-star chorus, including CCM industry "well-knowns": John Schlitt, Bob Hartman, LuLu Roman, members from the Winans family, Rick Cua, Kenny Marks, Lisa Bevill, Randy Thomas and Andy Denton.
Also released in March 2007 was a duet project by John Schlitt and Bob Hartman entitled Vertical Expressions, under the band name II Guys From Petra.