With more volatility than any other group, relievers can be the most frustrating assets for fantasy owners to manage.
Over the course of the season, many relievers go from being valuable producers one day to sitting on the waiver wire the next. Accordingly, wise owners will spread out their investment in the position -- drafting at least one elite closer and one mid-level option before taking a chance on another reliever with a late-round pick.
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Tier 1: Kenley Jansen, Craig Kimbrel
Jansen has established himself as the gold standard among relievers, posting a lifetime 2.08 ERA with a 0.87 WHIP and a 14.0 K/9 rate. With more than 40 saves in three of the past four seasons, the right-hander provides the best combination of excellence and reliability as the closer for the reigning National League champions.
Kimbrel wasn't far behind Jansen last year, recording 35 saves with a 1.43 ERA, a 0.68 WHIP and a 16.4 K/9 rate for the Red Sox. But after Kimbrel stumbled to the tune of a 3.40 ERA with a 5.1 BB/9 rate in '16, fantasy owners should give a slight edge to the Dodgers righty.

Tier 2: Roberto Osuna, Albertin Chapman, Corey Knebel, Raisel Iglesias, Felipe Rivero, Brad Hand, Edwin Diaz, Cody Allen, Ken Giles
Owners who pass on Jansen and Kimbrel would be wise to anchor their fantasy bullpens with at least one member of Tier 2, with Allen and Osuna representing the most stable options in this group.
Allen has posted a sub-3.00 ERA in five straight seasons and accumulated at least 30 saves in three consecutive campaigns. Meanwhile, Osuna has tallied 75 saves over the past two years and posted a 1.74 FIP behind his 3.38 ERA in '17. With better luck stranding runners this season (59.5 percent strand rate in '17), the right-hander could be a top five fantasy reliever.
Tier 2 also includes a quartet of bullpen arms who received an extended opportunity to handle the closer's role for the first time in '17. Knebel is arguably the most valuable of the four after tallying 39 saves -- this despite not collecting his first one until the middle of May -- and tying Kimbrel for first among full-time relievers with 126 K's. But Iglesias (28 saves, 2.49 ERA in '17), Rivero (21 saves, 1.67 ERA in '17) and Hand (21 saves, 2.16 ERA in '17) also have plenty of fantasy appeal.
Chapman, Giles and Diaz are the biggest boom-or-bust options in Tier 2. Chapman was a Tier 1 closer for several seasons before running into shoulder troubles and posting an uncharacteristically high 3.22 ERA last year. But with game-changing strikeout skills (career 14.8 K/9 rate) and the benefit of closing games for a talented Yankees club, the flamethrowing southpaw could lead the American League in saves if he experiences better health in '18. Giles will likely drop down many draft lists after struggling in the postseason, but he's coming off a stellar regular season (34 saves, 2.30 ERA) and is set to open '18 as the closer for the defending World Series champions. And while Diaz briefly lost his ninth-inning role during May and finished the season with an unimpressive 4.02 FIP, he also recorded 34 saves with a 3.27 and a 12.1 K/9 rate for the Mariners.

Tier 3: Alex Colome, Greg Holland, Wade Davis, Hector Neris, Sean Doolittle, Andrew Miller, Mark Melancon
The third tier presents a handful of enticing options for the second reliever spot on a mixed-league team.
Colome is the top option in this tier after leading the Majors with 47 saves last season. But with his name consistently popping up in trade rumors and the Rays lacking a potent lineup, the righty presents some risk for '18. The same goes for Holland, who tied Jansen for second in baseball with 41 saves last year but missed all of '16 and is still a free agent. Meanwhile, Davis has the skills (1.45 ERA, 0.95 WHIP from '14-17) to push into Tier 2 but will need to show he can handle Coors Field as well as Holland did last year.
Neris, Melancon and Doolittle are all potentially rewarding options, but each hurler comes with his share of risks as well. Neris had success in the closer's role last season, converting 26 of 29 save chances. But if the right-hander proves to be less effective than setup man Pat Neshek (1.59 ERA, 0.87 WHIP in '17), he may give new manager Gabe Kapler reason to rethink his bullpen arrangement. Melancon went into last season as a Tier 2 option after logging stellar statistics (147 saves, 1.80 ERA, 0.91 WHIP) from '13-16, but he is now tasked with rebounding from an ineffective and injury-plagued campaign. Finally, Doolittle has the talent and supporting cast to be a terrific fantasy stopper, but he's had trouble staying healthy across the past three years (104 innings combined).
Rounding out this tier is Miller, who has the ability (1.72 ERA, 0.79 WHIP, 14.5 K/9 rate from '14-17) to make a significant impact in all mixed leagues despite pitching in a setup role.

Tier 4: Richard Parker, Shane Greene, Brandon Morrow, Kelvin Herrera, Blake Treinen, Brad Brach, Arodys Vizcaino
Although owners would be foolish to grab all of their relievers from Tier 4, the members of this group could be serviceable second or third closers on mixed-league teams.
Morrow has a lengthy injury history, but he offers the highest ceiling in this tier after excelling (2.06 ERA, 0.92 WHIP) in a setup role with the Dodgers last season. Parker also has significant upside (2.54 ERA, 0.83 WHIP in '17), though he's compiled just 10 career saves and has yet to fully earn Angels manager Mike Scioscia's trust. Treinen was stellar late last season in Oakland (2.13 ERA), but he failed to capitalize on ninth-inning opportunities with Washington earlier in the year and has just 17 career saves. And Herrera struggled (4.25 ERA, 1.35 WHIP) in his initial season as a full-time closer, raising questions about his ability to hold onto the role.

Greene and Vizcaino are similar in that each has a firm grip on the closer's role but may not have the ability to rise above this tier. And finally, Brach (18 saves, 3.18 ERA in '17) can give fantasy squads a temporary boost until incumbent stopper Zach Britton returns to the Orioles this summer.