Iceland has a pretty high fuel tax, similar to many other western European countries. Visitors from Europe will find the prices comparable, but US travellers might find it a bit expensive. Here’s a service which gives you up-to-date prices in ISK.

There are petrol stations all over Iceland, but if you go to remote areas such as the West Fjords and the East Fjords, they might be a bit far between. If you’re travelling in remote areas, it might be a good idea to tank up when you see a station, as a rule of thumb.

Most stations have the choice of dealing with a human or using an automatic fuel dispenser. In more remote areas, there are famously some un-manned gas stations, where you can only use the automatic dispenser.

In this case it’s extremely important that your card works overseas and your credit card company knows you’re travelling. Some types of cards may not be accepted, such as Diner’s Club, and possibly American Express. Depending on the dispenser you may have the choice of using cash.

This is also sometimes the case in the middle of the night in more populated areas – you can use the automatic dispenser but there’s no person there.

One great trick is to get a gas card, where you pay in advance, and then know for sure that it will work. Most gas stations sell them, so just get one before you leave the city.

As far as I understand, if you choose a higher amount of money than you end up using, the automat will refund you the excess.

If you choose the “fill tank” option, it will reserve some relatively high amount of money (20.000 ISK or something) and then refund you the difference. Depending on the automat, this may take a shorter or longer time.