Taxi booking service Uber has reportedly been valued at nearly $51 billion, around £32 billion.
The valuation would mean the US-based company would equal Facebook's record for a venture-backed start-up.
It would also make Uber about as big as General Motors and larger than Netflix.
The valuation was reached after the firm's latest round of funding raised nearly $1 billion from Microsoft and Indian media company Bennett Coleman, among others.
The app has proved controversial in the UK and around the world.
Last summer thousands of taxi drivers brought London to a standstill in protest at how fares are calculated by Uber, claiming they illegally act like a meter.
The app has been banned in France and Germany.