If it is an oil and gas job then the tax will be deducted before you see the money as far as my understanding is i.e PAYE. The agency should take the tax out and pay you the rest. It is then up to you to claim a portion of it back at the end of the year.
The only exemption from Norway tax is if you do a cable lay job that is not Oil and Gas related i.e. Telecommunciations cable.
That is my understanding, can anyone clarify this that has recently worked in Norway?