PARADISE VALLEY, Ariz. -- A pitch clock will be used this season during minor league games in Triple-A and Double-A, but it has been ruled out for the major leagues this year.

Baseball commissioner Bud Selig said Thursday the decision to use the pitch clock in the minors followed a successful experiment in the Arizona Fall League.

MLB officials said details will be announced later, such as how much time will be allowed between pitches and other speed-up measures to be tested in the minors.

Speed-up rules cannot be put in place in the major leagues this year without approval of the players' union, and baseball officials said a pitch clock had been ruled out for this season

"We're in the midst of discussions with the union regarding potential changes," Selig said after his final owners meeting as commissioner, "so it's premature to discuss any details for this coming season at this point in time."

Selig said he is "very pleased with the progress we've made so far, but Yogi [Berra] once said it ain't over 'til it's over, so we're going to have to wait until it's over."

In the Fall League experiment, pitchers had to throw within 12 seconds with no runners on base and within 20 seconds when a base was occupied. There was a maximum of 2:05 between innings and a 2:30 limit for a pitching change. Additionally, hitters were required to have one foot in the batter's box at all times.

Selig is to retire Jan. 25 and be replaced by Rob Manfred.