Billions of dollars in government aid may not be enough to keep one or more of the major U.S. auto companies out of bankruptcy. 

One of the world's top ratings agencies, Standard and Poor's says both General Motors and Chrysler might collapse because of "highly uncertain consumer demand."

In restructuring plans presented to the U.S. government Tuesday, GM and Chrysler asked for a combined $14 billion in additional loans.  They argue bankruptcy could cost U.S. taxpayers more than $100 billion and millions of jobs at related companies.

Still, GM says there is a chance its Swedish unit, Saab, will not survive.

GM has been trying to sell Saab, and says the unit could go bankrupt by the end of the month without help from the Swedish government.

GM is asking for up to $6 billion in aid from several countries, including Sweden, Germany, Britain and Thailand.

German Chancellor Angela Merkel says her government needs to see a clear restructuring plan before it gives any money to GM.

Management and workers at GM's German unit, Opel, say they are working on such a plan.  Company officials also say they are willing to discuss alliances and partnerships with investors to avoid job cuts and plant closures.

GM's chief financial officer says the automaker continues to negotiate with workers and debt-holders in the United States in an effort to cut costs.

He says he expects talks on critical concessions will intensify now that the company has submitted a restructuring plan to the U.S. Treasury Department.

Some information for this report was provided by AFP Bloomberg and Reuters.