Can I buy an Oslo Pass at a Tourist Information in Oslor does one have to buy it online?
You can buy it at a TI. The one I bought it from sits close to the Radhus.
In 2003, when I went, I followed Rick's advice to buy it at the Tourist Information in the train station, which was hassle-free. My notes say that although my 3 day pass cost about $50, the things I did with it would have cost about $75. So, although you have to do the math as with any pass, it's an easy one to make pay off.