The loss compares to a post-tax profit of nearly VND300 billion last year.
With the amount of domestic fuel sold in the third quarter fell 9 percent year-on-year, the company saw revenues in the first nine months plunge 31 percent year-on-year to VND40.9 trillion.
Corporation leaders had said in June that fluctuations in oil prices this year have caused major difficulties for the oil giant. In April, Brent crude oil prices hit an 18-year low due to plunging demand globally.
The Dung Quat Oil Refinery in central Vietnam having to shut down for 51 days during the third quarter for maintenance added to the difficulties, they said.
The corporation had announced in June that it targets post-tax profits of VND376 billion this year, up 8 percent year-on-year.