Uber has now rolled out its service to more than 50 countries worldwide.

The fast growing taxi application service Uber has just finished its most recent round of funding which values the company at an impressive $51 billion; four times the valuation of Hertz ($7.8 billion) and Avis ($4.6 billion) put together.

Some of the companies involved in the funding include Microsoft and Indian Media conglomerate, Bennett Coleman & Co. The funding has raised nearly $1 billion just in the latest round increasing Uber’s external investment up to $5 billion.

Uber’s hunger for cash is based on its ambitious plans to expand. It is currently present in over 50 countries worldwide and is hiring drivers and accumulating more cars in order to cover the demand, whilst simultaneously paying for settlements of legal disputes with regulators and political lobbying. The rapid expansion of Uber has attracted investors globally.

Uber’s value has undoubtedly gained an extraordinary price tag; in comparison to tech start-up Snapchat, which has a valuation of $15 billion and AirBnb which has a valuation of $25 billion investors see the company as having huge potential. The tech-savy taxi company has also recently announced it plans to expand in India and invest $1 billion in ensuring its success.

However there are threats to Uber as workers challenge their status as independent contractors, some even taking legal action in order to gain employee status. The company originally kept its costs low by stating that they were a technology company in which it worked by pairing taxi drivers with customers and did not have the expense of vehicle maintenance, insurance and fuel.

Other challenges that have faced the company are allegations in Paris that the app matches customers with unlicensed taxi drivers and in New York the service has been halted along with other for-hire companies due to the concern about congestion and pollution.