What is green, has Minnesota roots and soared in value from $1 to $15 per share over the past year amid tremendous speculation about its born-again future? Before slipping back to Earth in recent weeks?

That would be Gevo, a public company that makes renewable fuel.

It historically was bigger on promise than performance, to the dismay of many out-of-patience investors who quit the company over the years.

But even at a recent price of $8.50 per share, Gevo is worth about $1.5 billion, has interesting plans and $500 million or so in expansion capital.

Gevo's CEO since 2007 is Patrick Gruber, an MBA and Ph.D. in chemistry out of the University of Minnesota. He was once a Cargill green-business executive.

Gevo has made ethanol and developed over several years a next-generation, low-carbon isobutyl alcohol that can be synthesized and used as a high-octane, cleaner fuel for cars and airplanes and in other products.

Gevo's death was predicted regularly for years. It sustained itself with ethanol sales and selling stock, which irritated existing shareholders through their dilution. Gevo also sold debt. The company was limping along as it tried to perfect its science and production, amid several setbacks at its plant in Luverne, Minn.

Last fall, Gevo's stock started to rise and volume increased amid encouraging news from the company. And Gruber's team, who didn't respond to a phone inquiry last week, has not been shy about predicting an enriching, less-polluting future. And it had been signing interesting deals with airlines, manufacturers and others.

"This will be a solution for greenhouse gases and the pollution that comes with fossil-based fuel products," Gruber said in 2019, at the time of a demonstration-project investment by Delta Air Lines.

This was shortly before Delta, in 2020, committed to an overall $1 billion investment over 10 years in "mitigating all flight and ground emissions from its global operations."

Gevo also has signed promising supply contracts with French fuels and polymers outfit Total and others.

Gevo's stock started moving out of the basement last fall. Investors also were inspired by President Joe Biden's commitment to fight climate change, partly with electric vehicles and cleaner transportation fuels.

Gevo quadrupled in value to $4.30 per share on heavy volume by year-end and soared above $15 for a day in mid-February. The company also sold more shares in two recent equity raises. And Gevo swapped $12.7 million in 12%-yielding notes held by Minneapolis-based Whitebox Advisors for 5.7 million shares.

Indeed, some of the exuberance has worn off among profit-taking investors this month. The stock has traded between $7 and about $10 per share, about where two analysts project it will end up this year.

Gevo shuttered its money-losing Luverne operation in 2020 and lost money on about $500,000 in revenue in the fourth quarter. Yet Gevo still is valued at a stunning $1.5 billion.

Gevo, which also has a small Texas operation, plans to build an $800 million-plus "net zero"-carbon plant on 240 acres in Lake Preston, S.D. That should produce, within three years, 45 million gallons a year of fuel and 400 million pounds of animal feed. The plant will be powered by wind and biogas.

"It shouldn't be lost on anyone that our business is significantly 'de-risked,' " Gruber told investors and analysts on a call this month. "We have money to execute our plans. Yes, it's quite a change from last year. Last year, we had to raise money to keep the lights on."

Gevo has plans for additional plants and an Iowa operation to convert cow manure into natural gas.

"We are off to a good start of this year," Gruber said. "Things are working and making progress. It's actually such a change and a blessing from last year. And now we are driving to get this done and get these plants online. Net-zero 1, and I want net-zero 2 and I want net-zero 3 as well."

This month, Gevo brought on board Paul Bloom, a scientist who spent 20 years at Archer Daniels Midland, the big grain-and-ethanol producer, as well as Evolution Chemicals, where he worked on a portfolio of renewable chemicals.

"Gevo has excellent technology to tackle greenhouse-gas emissions," Bloom said in a statement. "Drop-in, net-zero hydrocarbon fuel products are desperately needed and will make a difference in the transportation sector. And Gevo's renewable-chemical materials that can address … in the automotive industry, durable goods and consumer products."

Denver-based Gevo, which once lacked any support from Wall Street, is backed by securities firms H.C. Wainwright and Noble Capital.