CBS named CEO Leslie Moonves its chairman, replacing the 92-year-old Sumner Redstone. Viacom's board could follow suit and replace Redstone as chairman on Thursday, sources told CNBC.
Viacom and CBS shares rose 10 and 4 percent, respectively, in after-hours trading. Both stocks have lagged peers in the media space like Walt Disney in the last year.
"I think there may be some room for them to close the gap," said trader Tim Seymour.