This model dates back to the early days of N scale (late 60s / early 70s). Roco made a similar jumbo tank car around the same time (imported by Minitrix, et al).
I don't know what specific prototype this model might be based on (if any), but it looks a bit like ACF's 33,156 gallon tank car. The ACF "whale body" tank car was designed to haul liquefied petroleum gas (LPG) and anhydrous ammonia. Originally built in the early 1960s, you can still find these cars in service today.