Office-space startup WeWork lost $1.25 billion in the third quarter as expenses far outpaced revenue growth, draining the company’s cash ahead of a bailout by SoftBank Group Corp. last month.

We Co., as the parent company is officially known, said Wednesday in a report to debtholders that revenue surged 94% in the three months ended Sept. 30 to $934 million compared with the year-earlier period.

The report of the heavy dose of red ink compares with WeWork’s prior record loss of $638 million, posted in the second quarter, and is more than double the $497 million loss reported in same year-earlier period.

Behind the ballooning losses were many of the very concerns investors had with the company earlier this fall, when it attempted an initial public offering.

Once considered the most valuable startup in the U.S. with a valuation of $47 billion, WeWork’s attempt to go public was widely panned by potential investors given concerns over its mounting losses, as well as the erratic management style of the now-departed chief executive, Adam Neumann. With little apparent demand from investors, the IPO was pulled and Mr. Neumann was forced out.

For most of its existence, WeWork has been focused on revenue growth, impressing many analysts and observers with its ability to consistently double sales year after year.

But with the focus internally set on the top line, the nine-year-old company was never able to deliver its long-running set of pledges that it would rein in costs. Spending consistently rose, typically as fast as or even faster than revenue, as the New York company blanketed the world with glassy offices marked by a hip interior design and ample fresh cucumber water. The losses kept growing ahead of the IPO, at the very time that startups usually endeavor to show they are shrinking.

In the third-quarter report, WeWork said expenses rose at a faster rate amid rapid growth in areas like leasing costs and “new market development.” The latter is a wide-ranging category that included numerous areas of expansion pushed by Mr. Neumann, including a slew of tech companies WeWork acquired.