ガソリンが無くなりつつあります。

gasoline; petrol

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to be lost (e.g. luggage); to be missing; to be used up; to be run out; to be exhausted; to be consumed; to be reduced to zero; to not occur any more; to disappear (e.g. pain); to be lost (e.g. a dream, confidence)

while; even though; despite

to be (usu. of inanimate objects); to exist; to live; to have; to be located; to be equipped with; to happen; to come about