The possible endurance of a rebreather dive is longer than an open-circuit dive, for similar weight and bulk of the set, if the set is bigger than the practical lower limit for rebreather size, and a rebreather can be more economical when used with expensive gas mixes such as heliox and trimix, but this may require a lot of diving before the break-even point is reached, due to the high initial and running costs of most rebreathers, and this point will be reached sooner for deep dives where the gas saving is more pronounced.