Last year, the O's bullpen pitched more innings than any other team, 565.2. They weren't particularly good innings either, with a collective FIP of 4.31 and an ERA of 4.18, both of which were 4th worst in baseball.
A lot of this was the fault of the rotation. Pitching the least amount of innings by a significant margin (41.1 less than the 2nd to last Pirates) puts a terrible strain on the relievers. This year though, the SPs are doing a much better job of getting deep into games, pitching 228.2 IP so far, averaging just over 6 IP/GS. This is right in the middle of the pack.
But it hasn't been enough so far.
With all the extra-inning games the O's have played so far (an MLB leading 7) and with those games going deep into extras, the Orioles have already pitched 15 innings more than any other team. That strain is being put directly on the 'pen.
Somehow, the O's don't lead but are only second in relief innings (132.1, behind the Royals with 144.1) and 24 innings over average (108.1), while the median is just lower than that.
I would be worried by this since we saw what happens when a bullpen wears down but 12.1 IP were thrown by pitchers that aren't/ shouldn't/ won't be a real part of the bullpen this year so I'm not stressing out over those. Those pitchers are Eveland (4.2) (he might stay around if Lindstrom stays out), Chris Davis (2), Phillips (0.2), Berken (1), and Pomeranz (4). This means that the core of the 'pen (JJ, Strop, O'Day, Patton, Gregg, Ayala, Lindstrom) have pitched just 120 IP so far.
Strop leads with 21 IP. That puts him on pace for almost 90 IP. That should be a red flag for Buck as it might be too much work for a young reliever. The rest of the 'pen is fine, with only Ayala on pace for over 80 IP (81.1) and the rest on pace for less than 75.
Overall the bullpen has been worked hard (3.48 IP/G), mostly because of all the extra-inning play. But it seems Buck has been using his relievers efficiently, putting his best pitchers in the highest leverage situations. From highest to lowest average leverage (according to Fangraphs pLI): JJ, Strop, Ayala, Eveland (ESSS), Lindstrom, Gregg, O'Day and Patton. I'd say that's pretty damn close to a ranking of the O's bullpen talent with a minor tweak or two. This is what good starting pitching allows you to do. Keep it up Buck!