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General Motors sold about 10 million cars in 2016 for $9.6 billion in profit, accounting for 17.3 percent of all cars sold in the U.S., but on Monday, electric-car startup Tesla — 0.2 percent U.S. market share, 84,000 cars made last year — was briefly worth more money, despite having never turned a profit. After a Piper Jaffray analyst suggested that Tesla stock was undervalued, the company's share price rose to a high of $313.73, valuing Tesla at $51.5 billion, versus GM's $50.2 billion. Ford is worth about $44.6 billion, a mark Tesla passed last week. Tesla shares were valued at $40 in 2013.

Investors are betting that Tesla founder Elon Musk will deliver on the luxury carmaker's mid-range Model 3 arriving this year, with a base price of about $35,000, as well as consumer solar products. "Tesla's reputation as beyond-a-car company — it recently absorbed Musk's Solar City company for $5 billion — has captured the imagination of California's technology pack and, apparently, investors," The Washington Post explains. "The company has been developing batteries that could store power from rooftop solar panels, expanding its mission into a renewable-energy enterprise. Tesla also is exploring technology for self-driving cars."

Like all speculative investments, the bet on Tesla could deliver or flop, and Musk's electric-car enterprise has its skeptics. But even the doubters are impressed with what Musk has produced in a relatively short period of time. In the end, says Matthew Stover, an analyst with Susquehanna Financial Group, Tesla's heady rise "says a lot more about the stock market than it does about the auto industry."