A pillar of Venezuela's economy, PDVSA was in its heyday one of the five top oil companies on the planet. 

The state-owned enterprise has now failed to make interest payments on some of its debt, meaning it's entered "selective default," just like the government.

The fate of the company, founded in 1976, is closely tied to that of Venezuela, which is dependent on oil and sales of its heavy crude for some 96 percent of its export earnings.

Its bonds represent 30 percent of Venezuela's external debt -- estimated at around $150 billion -- which the government is seeking to renegotiate.

President Nicolas Maduro owes the difficulties to a fall in oil prices -- which have halved since 2014 -- and US government sanctions, which prohibit any US person or bank from buying the country's debt.