"It comes down to how much we would use Langerhans at this point," manager Don Wakamatsu said. "After these three games, and going into Texas with that hitter-friendly ballpark, it's probably not going to get any easier. We have to protect these guys now and long-term a little.
"We don't want to put stress on the bullpen this early in the season, and Colome brings depth and versatility in the bullpen."
Right-handers Mark Lowe and Brandon League, both used twice in the series, were unavailable for Thursday's series finale. Lowe threw 34 pitches in back-to-back games Tuesday and Wednesday nights while League threw 40 pitches on Wednesday night after throwing 15 in Monday night's season opener.
"When you get guys up to the 30- to 40-pitch count, you have to give them one or two days off," Wakamatsu explained. "That's why we needed to make this move today."
Colome joined the team early Thursday morning and pitched three innings, allowing three hits and two runs in the Mariners' 6-2 loss to Oakland.
"Colome came in and did a phenomenal job," Wakamatsu said. "He gave us the innings we needed and our bullpen is in great shape going into the next series [a three-game set against the Rangers in Arlington beginning Friday night]."
Wakamatsu said he prefers using Lowe, Sean White and David Aardsma no more than one inning at a time to keep them fresh, and the addition of Colome would make it easier to do that.
Colome, 32, has pitched in the big leagues in each of the past nine seasons, compiling a record of 19-26 with a 4.66 ERA over 328 relief appearances with the Nationals.
He also has pitched in the Oakland and Tampa Bay organizations.
The 30-year-old Langerhans appeared in one game with Seattle this season, flying out as a pinch-hitter on Wednesday night. He played in 38 games for the Mariners last season, batting .235 (22-for-101) with six doubles, three home runs and 10 RBIs. He hit a pair of walk-off home runs during the 2009 campaign -- Aug. 7 against Tampa Bay and Aug. 25 against Oakland.
Langerhans received the news around 10 a.m. PT, when he was called into Wakamatsu's office at the Oakland Coliseum.
"Anytime you have 11 pitchers, you know the chances of the bullpen getting stretched are there," Langerhans said. "You never expect that you will be the guy, so it was somewhat of a surprise."
Langerhans was acquired from the Nationals on June 28, 2009 in exchange for Mike Morse. He has appeared in parts of seven Major League seasons, combining to bat .232 with 27 home runs in 512 games.
He accompanied the team to Texas following Thursday's game, met his wife and drove to their home in Austin.
"The waiver period doesn't end until Monday," he said. "I hope to get claimed, but at the same time, I really enjoy it here. This is a good ballclub and good people, and I really wanted to be part of what's going on here."
If unclaimed, he said he probably would report to the Tacoma club.