He could get into a confrontation with a more powerful Murtagh and use Aren to kill Murtagh and steal the Eldunari he could just steal the Eldunari or he might use the energy to escape from the clutches of Galby himself I can't really think of anything else that he would use it for though I am sure I missed a ton.

Knowing CP's writting style I have a few Ideas...

1) To kill Galbatorix (Ya it's generic but...)
2) To heal someone important (Probably Aria or Nasuada)
3) To help Murtagh gain freedom from Galbatorix in some way

i am going for the third one myself, i like murtagh.

How would he use Aren to free Murtagh? Thorn and Murtagh are name slaves how would he change there true names with magic in the Aren?

Maybe he could cast a spell that directly counteracts what Galbatorix cast, then its just a matter of who has more energie? I don't know if even the energie in Aren would be enough to pull that off though...

How Galby is controlling Murtagh is not a spell he uses his true name to force him to swear oaths in the ancient language. He could also use the name to cast spells but even if Eragon broke these Murtagh would still not be free.

I dont think Eragon can save Thorn, probably Murtagh, but not Thorn.
Im pretty sure Galbatorix has Thorn's eldunari...

the energy could be used for anything eragon needs to do.

Yeah Tokenbrands right he's a lone(for now) Dragon Rider that aount of energy could come in handy many times over or just once

also your forgetting the vault of souls
it being a Vault he might need to break down amagical barrier of some sort

yeah fin makes a good point he will may need the energy for a barrier although solembum did say that speaking his true name would open it.

Yay i made a point
yeah i haven't read the 1st one in ages so i cant remember excatly what Solembum say so ill take your word for it
Well maybe he'll use it for something so simple we won't have been expecting it lol

when the time comes and you need a weapon look under the roots of the meona tree, also when you find your power insufficient go to the rock of kuthian and say your name to open the vault of souls. -solembum

that is almost exactly his words.

I think he will use it to finish off Galby.

Plain and simple lol
Yes its valid point but still.... its a bit too simple lol

yep short sweet and to the piont

Is it possible that the RoK is the stone in Aren?

no because aren has a gem in it not a rock.

Isn't a gem a kind of rock?

Not really. It depends how you define rock. When you say rock to most people they imagine something made of stone which a gem isn't made of.

I think that a gem can be considered a rock. People are saying that it might be Brom's tomb wich is made of diamond. Even though Brom's tomb won't be the RoK it could still be Brom's ring. Who knows how old the stone in Aren is.

1. By broad I meant if you take slang terms or the really broad geology definition which encompasses pretty much anything that wasn't at one stage living.

2. How could the ring guard the VOS if it's constantly moving? Don't say it's a key because then it's not protecting it's a way to get through the protection.

Do you have any ideas of what and where the RoK is?

A few but they aren't very likely and this isn't the topic for them.

wELL THE RING HAS A VAST AMOUNT OF ENERGY STORED IN IT SO IT IS PROBABLY GOING TO BE REALLY IMPORTANT IN THE FOURTH BOOK.(sorry about the uppercase letters. I didn't want to have to rewrite it all)

Agreed. But that dosen't mean it's going to open the VOS. It might be used to save Arya, Saphira or Nasuada or to kill Murtagh.

He probably won't use Aren until he faces Galby or if Murtagh gets unbelievably strong. Saphira wouldn't let him waste the power in there.

Is even Aren powerful enough to overcome all the Eldunari Galbatorix is likely to have on him?