Filling up a rental car overseas is mostly straightforward once you know a couple of local conventions.
Fuel is sold by the liter in most countries outside North America, with prices that often run higher than you'd expect. Confirm whether your rental takes petrol or diesel before you fill up, since mixing them up is still one of the most common rental mistakes worldwide.
Full-service stations remain common across parts of Europe, the Middle East, and Asia, where an attendant pumps for you and a small tip is customary. Self-service stations increasingly take card payment right at the pump, though rural stations can still be cash-only.
Return the car with the same fuel level you picked it up with, and hang onto the receipt — agencies often charge a steep premium for refueling a tank that wasn't topped off as agreed.