The sources asked not to be identified because the matter is confidential. CBS and Viacom declined to comment. Viacom's shares were down 3 percent at around $29.62 in after-hours trading, while CBS shares were little changed. CBS and Viacom have market capitalizations of $19.4 billion and $12.7 billion, respectively. CBS and Viacom set up special committees to explore the merger in February, a move to reunite the companies split by controlling shareholder Sumner Redstone more than a decade ago. The two companies explored a merger in 2016 instigated by the Redstone family, but those talks ended unsuccessfully, due to concerns by CBS about price and governance issues. Since then, Viacom CEO Bob Bakish has taken a number of steps to boost the company's performance, including improving relations with cable and satellite companies, causing some analysts to expect CBS to acquire Viacom at a premium.