"On n'a plus d'essence."
Translation:We're out of gasoline.
"We have no more fuel" should be accepted.
"Gas" is a North Americanism. We should accept "fuel" as a more universal/generic term. In most other English-speaking countries, it's "petrol" and gas would usually refer to "natural gas".
"Essence" = petrol (UK), gasoline (US), but also shortened to "gas" (US). "Fuel" is also accepted here. Depending on what you mean, "gas" may refer to "l'essence" (gasoline-US) or natural gas (gaz). In regard to "North Americanism", you make it sound like a bad thing. It is commonly used in the States just like "petrol" is used in the UK.
The audio on the normal speed is OK but the n’a is hard the distinguish from a. However on the slow version n’a is pronounced “naak” (sorry not good with the phonetic alphabet). Reported.
Yes, but often in oral French the "ne" is dropped. So even for negative sentences it may be said (but not written) "on a plus de..." meaning "we have no more."
However, it is still possible to distinguish between a spoken negative sentence and a positive one. In a negation, the "s" at the end of plus is not pronounced. In a positive statement the "s" is pronounced.
Here's a very helpful video about "plus."