BMW bosses have urged David Cameron to keep Britain in the EU as he toured the company's base in Munich.
The Prime Minister visited the headquarters during a trip to Bavaria where he appealed for German politicians to help with his membership renegotiation drive.
After meeting three British workers at the plant, Mr Cameron said he was "incredibly proud" that so many BMW cars had UK-made engines.
"BMW is a great example of how working together creates jobs and opportunities that benefit both our countries," he said.
"I am incredibly proud that so many BMWs roll off production lines with engines made in the UK
"I firmly believe the EU is stronger with Britain, and that Britain will be at its strongest in a reformed EU."
BMW's director for sales and marketing, Dr Ian Robertson, said the UK had the "most diverse car industry in Europe" and was the company's fourth largest market.
"From an industry perspective we would therefore regret seeing the UK leave the EU," he said.
"BMW Group has invested over £1.75 billion in the UK since the year 2000 across its four manufacturing plants and sources £1.2 billion worth of goods and services from UK suppliers annually.
"Together with our dealer network, we employ over 24,000 people directly while supporting nearly 50,000 UK jobs in the UK.
"In this context we believe it is advantageous for the UK to remain in the EU and to continue to be an active and influential member."
Mr Cameron has been attending the Christian Social Union's (CSU) annual conference in Bavaria, where he had informal talks with Chancellor Angela Merkel over dinner on Wednesday.
Mr Cameron said he believed there was "goodwill" to achieve a deal on changing Britain's membership terms - which he hopes to finalise at a Brussels summit next month before a decisive referendum potentially in June or October.
He stressed that the UK believed in the principle of freedom of movement, but insisted the public's concerns about immigration levels and exploitation of the welfare system needed to be addressed.
"My aim is very clear - I would like to secure the future of Britain in a reformed European Union but this reform is vital," he said.
"Britain supports the concept of free movement. Many British citizens can go and live and work elsewhere in Europe but we want to make sure that the welfare systems - and particularly our welfare system - is not an unnatural draw to Britain because we do feel the pressure of excessive migration that we've had in recent years."
Mr Cameron added: "The discussions are going well. They're hard, they're tough, these are difficult issues but I'm confident that with goodwill - and there is goodwill on all sides - we can bring these negotiations to a conclusion and then hold the referendum that we promised in our election manifesto and we've now legislated for in Parliament."
Mr Cameron is in Hungary later, where he will hold talks with counterparts Viktor Orban. He is hoping to enlist the PM's support for a four-year ban on migrants claiming in-work benefits - believed to be the major sticking point in a deal.
The men are also expected to discuss the migration crisis that has been wracking the continent, and has particularly affected Hungary.