Blackstone Group LP and Thomson Reuters Corp. are weighing an initial public offering or a sale of their stake in Tradeweb Markets LLC, which builds and operates electronic over-the-counter marketplaces, Bloomberg reported, citing people with knowledge of the matter.

According to the report, the companies have discussed the idea with bank shareholders, including Deutsche Bank AG, UBS Group AG and Royal Bank of Scotland Group PLC. The sources said Tradeweb, which is majority owned by Thomson Reuters, may be valued at over $4 billion in an IPO or sale, which would not occur until after Blackstone closes its purchase of Thomson Reuters's financial and risk unit.

A final decision has not been made, the sources said.