Vanguard Natural Resources LLC (VNR) has had a bad week. Despite its share price getting boosted to just over $1 last week by favorable oil prices, it has tumbled to nearly half that, currently at $0.58 per share. That’s down about 5% from yesterday’s close of $0.63. This down week comes in the midst of a bad 52-week period, as Vanguard's stock price has plunged from this time last year, when it was $8.94 per share.

Vanguard announced on Monday that it would delay a $15 million interest payment on some of its senior notes, taking advantage of the grace period on the payment. On Wednesday, when the payment was due and still unpaid, the stock fell 30%, sparking fears about the overall health of the company.

If payments on these senior notes are not made within the 30-day grace period, Vanguard would default on its entire debt – not just the $381.8 million in senior notes – and almost certainly be forced into bankruptcy.

On Sept. 20, Reuters reported that Vanguard had hired Evercore Partners to explore restructuring options. Vanguard currently has $1.8 billion in debt, including $1.4 billion drawn from its revolving credit line. Yahoo Finance estimates Vanguard's enterprise value at $1.95 billion and its total assets at $358.5 million.

In May, Vanguard sold one of its more promising assets – 25,000 acres of oil-rich land in the SCOOP/STACK plays – for $280 million. Vanguard used that money to pay down its bank debt in order to give it some breathing room and improve its borrowing base, which lenders had reduced from $1.78 billion to $1.325 billion. As of the second quarter of this year, Vanguard had total borrowings of $1.394 billion, leaving it $68.5 million over its adjusted base. (See also: Vanguard Natural Resources Gets Well-Timed Break.)

Unless Vanguard can address its liquidity problems quickly and cover the debt payment in the grace period, the future for this upstream oil producer could be pretty grim.