The owners of the UFC are moving forward on to the next steps in the process of selling the UFC.

ESPN reported the news on Tuesday that the “owners are in advanced talks to sell the business.” ESPN’s sources say that there are four serious buyers in the mix to purchase the UFC including WME/IMG, China Media Capital, The Blackstone Group and Dalian Wanda Group.

The UFC is privately owned under the parent company Zuffa so their financial information does not have to be disclosed. However, Lorenzo Fertitta told CNN last year that the UFC brought in about $600 million in revenue in 2015.

Check out the video report from ESPN going into detail regarding the sale of the biggest MMA promotion in the world that has a valuation estimated between $3.5 billion and $4 billion.