According to Crain's New York Business, Vroom has just restocked its war chest as it fights to extend e-commerce to the used-car category.

On Friday, the six-year old company, which buys and sells vehicles through its website across the country, announced that it has raised $254 million in a Series H round, bringing its funding total to $721 million. The round was led by newly-formed Durable Capital Partners, based in Washington, D.C.

The size of the round indicated both investor-interest in the potential for online used-car sales, and the capital-intensive nature of the venture. Vroom, which has offices in Midtown and operates a 350,000 square-foot reconditioning facility outside of Houston, will use the money to expand an e-commerce product- and engineering-hub it opened in Detroit this summer.

In an interview, Vroom CEO Paul Hennessy, a former head of Priceline, declined to disclose sales figures, but said they were growing by "triple-digit" percentages.

"That's giving us all the signals" of enthusiasm among consumers, he said.

Vroom's competitors include used-car giants Carvana and CarMax, but unlike them it has no brick-and-mortar presence. Hennessy said the industry overall generates $780 billion in annual revenue, and that it's ripe for a new way of doing business.

"There are 43,000 used-car dealerships," he said. "That's who we're really competing against."

He added that the market is "massively fragmented," with the largest players having less than 2% market share.

Analysts say consumers have been learning to buy everything online over the years, and that car buyers may end up preferring the e-commerce experience to visiting a car lot and negotiating with a dealer. But the costs involved in reconditioning cars and transporting them make the business equation more complicated than it is for selling clothing or electronics.

"It won't be long before this becomes a fairly significant way that people purchase cars," said Mike Ramsey, automotive analyst for Gartner Research. "The question is can you make money doing it."