Opel and Vauxhall decision looms
Opel and Vauxhall employ about 50,000 people in Europe
It has been widely reported that General Motors (GM) has chosen the Canadian car parts manufacturer Magna to buy Opel and sister firm Vauxhall. GM is expected to make an announcement later in the day and is understood to have attached conditions to the sale.
Earlier, there were rumours that GM could be planning to try to keep control of its European arm.
Magna is the German government's preferred bidder. Any decision will have to be approved by the Opel Trust.
It has called its own news conference in Berlin at 1615 (1415 GMT).
The German-led Opel Trust has controlled the European operations since GM sought bankruptcy protection in the US.
It contains representatives from GM, the German federal government and the German states that contain Opel plants.
The rival offer came from the Belgian investment group RHJ.
Opel employs a total of 54,500 workers across Europe, with 25,000 based in Germany.
Its Vauxhall brand employs 5,500 people in the UK, primarily at its two British plants in Luton and Ellesmere Port.
Unions in the UK say that GM keeping control of Vauxhall would be the best news for British jobs.
The German government has said that GM would have to repay its 1.5bn euro ($2.2bn; £1.3bn) loan.
"The 1.5bn-euro bridging credit is a loan. And a loan is a loan. GM must pay back the 1.5bn under the conditions that we agreed on for Opel," German Finance Minister Peer Steinbrueck said on Wednesday.
He also said that there would be no more government help for GM if it closed German factories.
It is not clear where GM would get the money it would need to hang on to Opel.
GM emerged from 40 days of bankruptcy protection in July, based on a plan involving disposing of many of its brands. It is now 61% owned by the US government.
Last month, GM failed to choose between Magna and RHJ's initial bids, leading to speculation that the sale would not happen, for fear of technology and engineering resources ending up in a competitor's hands.
The German government prefers the Magna bid, based on the two companies' plans for job cuts at Opel following the takeover.
Both will see significant cutbacks in the workforce, but Magna is proposing fewer job cuts in Germany.
Nearly 25,000 people are employed at Opel's four plants in Germany, so the country has a strong interest in the outcome of the takeover, especially with a general election taking place in Germany later this month.
There is also understood to be pressure to find a solution in order to avoid distracting attention from model launches at next week's Frankfurt Motor Show.