The companies said in separate statements Thursday that their boards have formed exploratory committees to mull a deal. Viacom said it has hired outside legal advisers and will hire bankers.
Statements from both companies said, "There can be no assurance that this process will result in a transaction or on what terms any transaction may occur." They also said they wouldn't comment further, "until the process is completed."
A combination of the two, which were split more than a decade ago by the media mogul Sumner Redstone, is being orchestrated by his daughter Shari. It would combine CBS's broadcast television network with Viacom's cable channels and film studio amid a big shakeup in the industry.