Elon Musk’s tunneling venture The Boring Company is negotiating to secure a $4 billion funding round at a valuation of $20 billion, as reported by The Wall Street Journal.

The agreement is yet to be finalized and the conditions may shift, according to the WSJ. At a $20 billion valuation, it would represent a substantial increase from The Boring Company’s $5.7 billion valuation in 2022.

The startup has constructed a network of tunnels beneath Las Vegas, allowing Teslas to transport customers to various stations. However, tunnel workers have experienced serious injuries, and Nevada regulators stated last year that The Boring Company breached environmental regulations nearly 800 times.

The Boring Company has revealed intentions to create tunnel systems under Nashville and Dubai. The WSJ notes that the startup has also proposed projects in Baltimore, Chicago, and Los Angeles.

The startup originated from SpaceX in 2018. SpaceX recently achieved the largest IPO to date, although its stock price has seen a notable decline since then.