There are and have been several bands named Gehenna, the most notorious of which are the following: 1) A black metal band from Norway. 2) A blackened hardcore band from Reno, Nevada, USA (also known as THE INFAMOUS... GEHENNA)
1) Oblivion is a technical death metal band from California, USA that formed in 2007 by members(and ex-members) of Antagony, Alchemicon, All Shall Perish and Feast.
There are mutliple artists with this name: 1) Lifeless was a 90s straight edge hardcore/metalcore band from Salt Lake City, Utah formed in the fall of 1995. They realeased one self-titled 7" on Life Sentence Records in 1996. http://www.myspace.com/lifelesssaltlake