An arrangement for providing liquefied natural gas (LNG) as fuel for propulsion of a ship (1, 6) having cargo tanks (2, 7) for liquefied gas comprises a source of LNG (3, 8) and at least one first heat exchanger (41) for vaporizing and/or heating the LNG directly or indirectly with a warmer medium (44). The warmer medium is boil-off gases from the cargo tanks (2, 7) being re-liquefied in the process.