Shares in Uber fell around 6% after the company reported record losses for its second quarter.
The $5.24bn (£4.3bn) net loss was significantly wider than its $878m (£723m) loss at the same time last year.
Costs rose by 147% to $8.65bn (£7.1bn) during the quarter.
This was partially due to one-off costs, such as $3.9bn (£3.2bn) of stock-based compensation expenses related to its IPO earlier this year and nearly $300m (£247m) in “driver appreciation” related to the stock sale.
But there was also a sharp rise in spending on research and development.
Total revenue was up 14% to $3.2bn (£2.6bn) but still below expectations.
Revenue from the company’s main business – its ride-hailing – grew just 2% to $2.3bn (£1.9bn) and food delivery division Uber Eats grew 72% to $595m (£490m).
Haris Anwar, analyst at financial markets platform Investing.com, said: “Losses are widening and the competition is cut-throat.
“What’s sapping investor confidence and hitting its stock hard after this report is the absence of a clear path to grow revenue and cut costs.”
Chief executive Dara Khosrowshahi insisted the losses would diminish in 2020 and 2021 while the company invests aggressively.
The competitive environment is starting to rationalise and has been “progressively improving”, he said, adding that the business would eventually become profitable.
Uber’s monthly active users rose to 99 million globally, from 93 million at the end of the first quarter and 76 million a year earlier.