Major League Baseball this week announced plans to expand support for Apple's Passbook mobile ticketing app, which will be accepted at 13 ballparks this season. As GigaOm reports, this marks a rather significant expansion from 2012, when just four teams — the San Francisco Giants, New York Mets, Boston Red Sox and Kansas City Royals —supported the app.

Beginning this summer, the Baltimore Orioles, Chicago Cubs, Detroit Tigers, Milwaukee Brewers, Minnesota Twins, Oakland Athletics and Pittsburgh Pirates will all accept paperless tickets through Apple's Passbook app for iOS 6. MLB says three other teams will also support the app, though they're not yet ready to make it official.

MLB was one of the first to support Passbook when Apple announced it last year, joining other companies like Starbucks, Fandango, and United Airlines, among others. Bob Bowman, CEO of MLB Advanced Media, told MarketWatch last year that the organization was "floored" by fan feedback after launching Passbook in September 2012, noting that 12 percent of all e-tickets were purchased through Apple's app.