Selig made the announcement during an interview on "The Mike Lupica Show" on ESPN New York radio on Friday.
"We're now going to add it on trapped balls in the outfield and as I call them bullets down the right and left field line," Selig said.
Currently, replay is only used on home runs to determine whether a ball clears the fence or is fair or foul.
Selig did not say when replay expansion would begin. He said he will continue reviewing the policy and that he was "very cautious" about making the changes. The commissioner said he was concerned about how expanding replay would affect the pace of the game.
Selig also addressed those who feel that expanding replay is ruining the purity of the game.
"There are some people who believe that by going to the last two things, maybe I've gone too far and I don't think so," Selig said.