Once again, bla bla bla awesome song, bla bla bla I play this in CGCGCC with power 
chords. I suggest you do the same, 'cause some JBT songs are good in standard...
but others are truly better in open C. If this seems a bit easy and lacking,
I suggest you have a look at the tab that Largebehind put up here on UG. 
It's pretty much spot on.
NOTE: the song is apparently played with a capo on 4th, so the scales are E minor and B 
minor with the same chords as below, but I like it without (lower pitch, deeper sound).

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                     Oldman - John Butler Trio
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Tabbed by: DarrenJag
E-mail: jasperjmarcus@gmail.com
Scale: C minor for verse, G minor for chorus

Intro:         Gm  Eb  Cm  Cm
Verse:         Cm  Ab  Fm  Fm
Prechorus:     Gm  Eb  Cm  Cm
Chorus:        Gm  Bb  Eb  Cm
(for the second, powerful chorus, don't be afraid to batter your strings! :D )

(clean)
Cm                         Ab        Fm
Old man he looks out the window,
You know he gets quite a fright,
The whole world has gone and changed on him,
Feels like it was overnight,
He saw a world war yeah it came and went,
The man walked on the moon right there in his living room,
Saw that TV become a religion,
The Wall came down and Big Mac beat the communists and,

(overdrive)
Gm                  Eb            Cm
Feels like it was overnight, oh god it,
Feels like it was overnight,
Feels like it was overnight, oh god it,
Feels like it was overnight,

(clean)
Cm                      Ab          Fm
Old man looks out the window,
You know he can not open it anymore.
The air outside its gone to rancid,
And the doctor said for him you know it wouldn't be so good for,
He saw a hole start opening up in the sky,
He's buying water man he doesn't even know why,
The smog alerts don't let him even go outside,
And then he starts to wonder when the Earth it started to die,

(overdrive)
Gm                  Eb            Cm
Feels like it was overnight, oh god it,
Feels like it was overnight,
Feels like it was overnight, oh god it,
Feels like it was overnight,

(slow, overdrive)
Gm Bb Eb Cm
            Enjoy your last.
            Last taste of freedom!

(clean)
Cm                          Ab        Fm
Old man he bars up the windows,
You know he does not feel so safe anymore,
He comes from those supposed good ole days,
When you did not even have to go lock your doors,
He saw security man look like police man,
Saw the police start looking like the army man,
He saw the army start acting like the C.I.A.,
And guess what, the C.I.A. was the president,

(overdrive)
Gm                  Eb            Cm
Feels like it was overnight, oh god it,
Feels like it was overnight,
Feels like it was overnight, oh god it,
Feels like it was overnight,

(powerful, overdrive)
Gm Bb Eb Cm
            Enjoy your last.
            Last taste of freedom!