In the greater Reykjavík area gas stations are open Mon-Sat 07:30-20:00, Sun 09:00-20:00 (Oct- May 10:00-20:00). Many gas stations in the Reykjavík area have automats in operation after closing, they accept bank notes (minimum is set at 1000 ikr.) and credit cards.
Opening hours around the country, where the pumps are privately operated, can vary from place to place. Most stations are open until late in the evening, to 22:00 or even 23:30.
All gas stations accept credit cards. Automats are also operated in various places around the country. Octane levels in Iceland are 92 regular unleaded, 98 premium leaded and premium unleaded 95.
Since Iceland is sparsley populated it can sometimes be a long distance between gas stations. For an example no gas stations are located in the highlands so it might be a good idea to have extra fuel cans from AB Car rental while driving in areas where the towns are few and far between.