What happened 

Shares of hydrogen fuel company Plug Power Inc (PLUG -4.93%) plunged 16.8% in November, according to data provided by S&P Global Market Intelligence, after reporting another big quarterly loss. 

So what 

Third quarter net revenue doubled to $35.4 million, but net loss more than tripled to $41.0 million, or $0.18 per share as the cost of stock warrants weighed on the company's financials. 

Hydrogen symbol made with leaves on a floor.

Image source: Getty Images.

What's worrying investors is that deals with Walmart and Amazon may weigh on results for the foreseeable future. Management said they need to maintain a high level of performance in the fourth quarter, which they said will be a high risk. 

Now what 

Plug Power doesn't have much room for error fulfilling its growing order book because its operating margins have been negative for a long time and management hasn't proven they can turn the trend around. If losses continue it'll force management to sell shares to fund operations, continuing a long-term trend of diluting shareholders. Until Plug Power turns operations around and starts making money I'll remain skeptical on this stock and investors should be cautious as well.