"We are lowering our long-term issuer ratings on Petroplus to CC from CCC+ to reflect our view that the risk of a near-term payment default has increased," S&P said in a statement.
"The ratings remain on CreditWatch, where they were placed with negative implications on December 29."
S&P said the cut reflected new concerns following an announcement by Petroplus that all of its credit lines under a secured credit facility have been suspended.
"We understand that Petroplus has met with its lenders but that no long-term solution has yet been reached," S&P said.
The situation became critical on January 5th after Petroplus, the biggest independent oil refiner in Europe, indicated that banks had frozen all credit lines which forced the closure of some of its plants.
Petroplus announced on December 27th it had been denied a credit line of $1 billion deemed "indispensable" to the proper functioning of its operations for the purchase of crude oil.