Magna must still get German government clearance for the deal
Late-night talks are continuing in Berlin as US and German officials seek a takeover of Opel and Vauxhall, parts of General Motors' European division.
Talks with a preferred bidder, Canadian car parts maker Magna International, "are going well", Reuters news agency quoted a German official as saying.
Earlier, Magna briefed UK Business Secretary Lord Mandelson, who said a deal was "pretty close".
The US parent firm is expected to file for protective bankruptcy on Monday.
General Motors, one of the world's largest carmakers, has been stricken by a collapse in demand for new cars amid the global recession.
General Motors executives successfully agreed a major cost-saving deal with its workers on Friday to pave the way for a major restructuring of its business.
UAW members voted to give GM in the US 'a lifeline'
Three-quarters of all United Auto Workers (UAW) union members voted to accept a freeze on pay and an end to bonuses - cutting labour costs by up to $2bn a year, the union said.
It also agreed to cut health benefits to retired employees.
Instead of the company funding health care costs for former workers, the union health trust will do so. The union will take an ownership stake in return for absolving GM of its responsibilities.
UAW also agreed not to strike until 2015 in a bid to shore up the company and save jobs.
"Their shared sacrifices will enable GM to become a stronger, more viable company that will continue to deliver world-class cars and trucks," said Diana Tremblay, GM vice-president of labour relations.
Despite the concessions, 21,000 jobs are expected to be lost and several plants will be closed in the US.
"We've given a lifeline to GM until they can rebound," said Ron Gettelfinger, UAW president.
By 1 June, ownership of the US based business is expected shared between the US government (72.5%), the union's health trust (17.5%) and GM's former creditors.
Mandelson sees 'positive' GM deal
While GM will ultimately choose who buys Opel and Vauxhall, the German government's preference is key because Berlin has pledged the most financial support for the eventual buyer. About half of GM Europe's 50,000 workers are employed in Germany.
The other potential bidder, Fiat, did not attend Friday's talks with the German government, saying Berlin's position was "unreasonable" though it is not yet clear if Fiat had pulled out altogether.
Speaking to the BBC, Lord Mandelson said that after Magna tabled its offer, they came to London for a meeting.
"They made it absolutely clear that they would be committed to continued production by Vauxhall in the UK," he said.
"It looks as if GM in Europe can be saved. Of course it will involve change, there is excess capacity," Lord Mandelson said.
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