Commercial interest in the diesel engine was intense. Scottish engineering firm Mirrlees, Watson, & Yaryan Co had an early interest in the diesel engine and was the first non-German firm to make a licensing agreement. The company's co-founder, Sir Renny Watson, invited Diesel to London to demonstrate his engine and grant Mirrlees, Watson, & Yaryan Co exclusive manufacturing rights in the UK. Diesel found the negotiation process exhausting and eventually agreed to have Lord Kelvin (the world's foremost expert in thermodynamics who developed the Kelvin temperature scale) review the patent and evaluate the design. Lord Kelvin quickly recognized how invaluable the cold start of the diesel engine would be to military applications. In March 1897, Diesel signed the licensing agreement; he would be paid 100,000 marks, and a 25% royalty on all sales. This agreement marked the beginning of the global proliferation of the diesel engine.

Adolphus Busch, the German-American beer magnate of Anheuser-Busch fame, was a proponent of technological innovation. On a trip back to his native Germany, Busch heard about Diesel's new engine and was intrigued. He sent Colonel E. D. Meier, a fellow German immigrant and veteran, to view a test of the engine. Meier was impressed, so Busch invited Diesel to a resort town in Germany and happily paid Diesel one million marks to have the exclusive rights to manufacture and market diesel engines in North America.