What happened

For the fourth day in a row -- the fourth day since its initial public offering -- shares of electric car upstart and purported Tesla-killer Rivian Automotive (RIVN 8.05%) marched higher Tuesday.

Through 10 a.m. EST, Rivian shares have already gained another 6.3% despite there being no new news today to explain the enthusiasm.

A green stock arrow rises higher.

Image source: Getty Images.

So what

No new news about Rivian, that is to say. As it turns out, though, one of Rivian's competitors in the electric vehicle space, Lucid Motors (LCID 25.00%), just reported its third-quarter 2021 earnings last night -- and it seems investors are pretty excited about that one.

Although Lucid reported wider losses and lower sales than anticipated, investors responded positively to the luxury electric car maker's announcement that its Lucid Air sedan just won Motor Trend's Car of the Year award. They were also pretty pumped to learn that Lucid booked 13,000 reservations for new car sales in Q3 -- and grew that number past 17,000 over the six weeks since Q3 ended.  

And Lucid was able to announce that it has begun producing vehicles to fulfill all those orders at its Advanced Manufacturing Plant ("AMP-1") in Casa Grande, Arizona, where a "second phase of construction" has already begun to add 2.85 million square feet of manufacturing space.

Now what

All of this speaks to the heady pace at which electric vehicle adoption appears to be taking place, a fact that bodes well for both Lucid and Rivian (and Tesla, too, of course).

All that being said, I still think investors need to be cautious about these companies, which now carry market capitalizations of more than $76 billion (for Lucid) and nearly twice that -- $141 billion -- for Rivian. Suffice it to say that seems an awful lot of money to pay for a dream, no matter how fast it's materializing. The more so when you consider that until these companies start booking some sales, and reporting some profits, you can't possibly know what kind of profit margin they will be earning on their cars.

Until that happens, you may know the price of Lucid and the price of Rivian -- but you won't know the value of either one of them.