U.S. electric-vehicle startups saw massive weekly gains on Friday after a searing rally in their shares over the past few sessions nearly doubled the value of companies such as Nikola.

The surge in EV stocks has come without any apparent news or catalyst for the companies, leading several analysts and traders to point to a potential squeeze in the highly shorted stocks.

For instance Lordstown Motors has a short interest of 16.5%, according to S3 Partners. Other big gainers such as Nikola and Workhorse Group have short interests of 21.7% and 23.9%, respectively.

Used-car retailer Carvana, another highly shorted stock, has also posted strong gains that have pushed up its value by nearly $1.38 billion this week.

“We see this every time the market gets hot,” Dennis Dick, a trader at Triple D trading, said.

“Carvana probably kick-started this, it is up more than 100% in a couple of weeks on a short squeeze. Smaller names with high short interest are following suit now.”

The gains have added more than $400 million to the collective market value of the EV startups and coincided with a record winning streak at market leader Tesla, whose stock movement often influences other companies in the sector.

RETAIL INTEREST

Retail investors have also ploughed into EV shares, with the J.P. Morgan retail flows tracker showing Nikola was the fifth most traded U.S. stock by such traders on Thursday.

Nikola and Lordstown have drawn a flurry of bullish options activity in recent days as traders place bets on further gains.

On Thursday, more than half a million options contracts on Nikola changed hands, making the relatively small company the eighth most active single stock name in the options market, according to Trade Alert data.

The stock surge could help Nikola overcome the risk of being delisted after it received a warning late in May from Nasdaq that its share price had been below the $1 minimum level.

Nikola fell 15% on Friday and closed at $1.19. Despite the drop, the stock is on course to stay above the minimum level for the third straight session.

The stock will regain compliance with Nasdaq’s norms if it trades above $1 for 10 consecutive days.

Workhorse rose nearly 1% and Lordstown fell about half a percent, while Carvana was down about 4% at the end of a week in which it has gained more than 30%.

Nikola’s stock has a 12-month forward price-to-sales ratio of 3.21, compared with Workhorse’s 1.38 and Tesla’s 7.23, according to Refinitiv data.

Still, many challenges remain for the EV startups.

Rising interest rates and high inflation have limited their access to funding at a time when efforts to ramp up production are already thinning the companies’ cash reserves.