Hello
Similar:
http://www.whatfontis.com/Allumi-Std-Extended-Heavy-typofonderie.font?te...
Alex
I found it using: http://www.whatfontis.com - Identify the font you are looking for!

Maybe it is custom made, but does anyone have a clue?

I'm sorry, I don't know any font with such a /O but I can't state it's custom made. May be it is as simple as "generic extended sans like Helvetica/Akzidenz Grotesk with a custom /O".
What I can propose though:
- the logo itself, freely available to download as vector: http://www.brandsoftheworld.com/logo/only-denim
- some similars: Foundry Monoline, NeoGram, Sui Generis (which comes very close, for the /NLY part at least), Forza
- a possible track to follow: have a closer look to the /® (register mark), the external circle and /O look like to share the same design. /R reminds me once again of Foundry Monoline. So my last call: custom job based on Monoline.

Thanks guys for you help it properly is custom made, but i've got some good alternatives ;)