MEXICO CITY (AP) ¿ Standard & Poor's Ratings Services cut its rating on Petroleos de Venezuela SA on Friday, citing concern about the state-controlled energy company's willingness to pay suppliers.

The ratings agency downgraded the Caracas, Venezuela-based company to "B+" from "BB-," both of which are junk status. S&P kept a negative outlook, implying further downgrades are possible.

The lower the outlook, the harder it is generally for companies to obtain financing.

"The downgrade reflects the company's tighter liquidity and, in our view, a heightened uncertainty regarding its willingness to meet its contractual obligations with some of its suppliers," S&P said in a statement.

Petroleos de Venezuela, which owns the American refiner and gas station chain Citgo, is controlled by President Hugo Chavez's Venezuelan government.

The company, also known as PDVSA, has accumulated debts with both foreign and domestic oil contractors that reached $7.6 billion as of last December. But the company has since paid more than one quarter, or $2 billion, of that amount, and will continue to pay what it owes, Oil Minister Rafael Ramirez said recently.

In the past month, Chavez's government has nationalized more than 74 oil contractors under a new law, seizing natural gas compression facilities belonging to Tulsa, Okla.-based Williams Companies Inc. and Houston-based Exterran Holdings Inc., as well as Venezuelan companies that operated boats and docks on western Lake Maracaibo.

Ramirez said PDVSA will not consider joint enterprises with those companies: "We're taking these over for the state ¿ 100 percent," said recently.

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