Aroldis Chapman has the highest career K/9 when pitching at least 500 innings, with 14.58 per nine innings.

	NAME	K/9	IP	G	W	L	W%	GS	ERA	SO	CG	SHO	SV	H	ER	R	HR	BB	HBP	GF	IBB	TBF	WP	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	ERA-	FIP	FIP-	H/9	PRAA
1	Aroldis Chapman A. Chapman	14.58	821.1	863	60	47	.561	0	2.52	1,331	0	0	367	475	230	255	54	408	33	563	7	3,341	87	4.47	3.26	0.59	39.8	12.2	1.08	.278	2.79	61	2.36	57	5.20	161.8
2	Josh Hader J. Hader	14.56	512.1	468	34	31	.523	0	2.64	829	0	0	226	282	150	164	65	198	24	321	6	2,019	19	3.48	4.19	1.14	41.1	9.8	0.94	.240	2.88	64	2.88	69	4.95	75.7
3	Edwin Díaz E. Díaz	14.54	519.1	520	28	36	.438	0	2.82	839	0	0	253	356	163	176	54	182	40	395	9	2,105	33	3.15	4.61	0.94	39.9	8.6	1.04	.305	3.05	70	2.55	61	6.17	93.4
4	Craig Kimbrel C. Kimbrel	14.04	821.2	851	56	48	.538	0	2.58	1,282	0	0	440	492	236	263	75	346	40	656	11	3,306	70	3.79	3.71	0.82	38.8	10.5	1.02	.267	2.88	63	2.60	64	5.39	131.8
5	Kenley Jansen K. Jansen	12.40	927.1	934	54	40	.574	0	2.57	1,278	0	0	475	610	265	284	88	282	32	700	20	3,680	21	2.74	4.53	0.85	34.7	7.7	0.96	.261	2.76	65	2.62	64	5.92	147.2
6	Billy Wagner B. Wagner	11.92	903.0	853	47	40	.540	0	2.31	1,196	0	0	422	601	232	262	82	300	33	703	26	3,600	43	2.99	3.99	0.82	33.2	8.3	1.00	.261	2.61	54	2.72	63	5.99	159
7	Brad Lidge B. Lidge	11.92	603.1	603	26	32	.448	1	3.54	799	0	0	225	492	237	257	57	287	34	368	41	2,589	46	4.28	2.78	0.85	30.9	11.1	1.29	.308	3.83	82	3.26	75	7.34	72.7
8	David Robertson D. Robertson	11.83	894.1	881	68	46	.596	1	2.93	1,176	0	0	179	674	291	315	81	365	25	358	38	3,690	57	3.67	3.22	0.82	31.9	9.9	1.16	.290	3.17	70	2.98	70	6.78	122.3
9	Carlos Marmol C. Marmol	11.60	577.0	519	23	35	.397	13	3.57	744	0	0	117	385	229	242	49	395	51	259	22	2,521	35	6.16	1.88	0.76	29.5	15.7	1.35	.262	3.77	85	3.95	94	6.01	15.6
10	Jake Diekman J. Diekman	11.42	602.1	705	27	34	.443	0	3.91	764	0	0	19	483	262	312	53	358	47	141	21	2,662	44	5.35	2.13	0.79	28.7	13.4	1.40	.299	4.66	95	3.77	91	7.22	23.8
11	Shohei Ohtani S. Ohtani	11.41	528.2	100	39	20	.661	100	3.00	670	1	1	0	388	176	184	56	182	24	0	2	2,139	52	3.10	3.68	0.95	31.3	8.5	1.08	.275	3.13	71	3.17	74	6.61	62.1
12	Tyler Glasnow T. Glasnow	11.36	754.0	167	43	36	.544	128	3.74	952	0	0	0	575	313	333	94	290	13	9	5	3,085	63	3.46	3.28	1.12	30.9	9.4	1.15	.277	3.97	91	3.47	83	6.86	59.4
13	Blake Snell B. Snell	11.19	1158.0	222	81	62	.566	222	3.15	1,440	1	1	0	891	405	440	111	521	11	0	6	4,791	86	4.05	2.76	0.86	30.1	10.9	1.22	.288	3.42	77	3.31	79	6.92	111.7
14	Freddy Peralta F. Peralta	11.15	931.0	211	70	42	.625	162	3.59	1,153	1	0	1	694	371	392	118	360	48	6	3	3,853	31	3.48	3.20	1.14	29.9	9.3	1.13	.265	3.79	85	3.66	87	6.71	59.2
15	Chris Sale C. Sale	11.14	2084.0	393	145	88	.622	312	3.01	2,579	16	3	12	1,692	697	750	213	487	130	25	15	8,389	48	2.10	5.30	0.92	30.7	5.8	1.05	.297	3.24	70	2.87	68	7.31	303.3
16	Greg Holland G. Holland	11.13	547.2	556	30	28	.517	0	3.14	677	0	0	220	417	191	211	43	241	7	355	20	2,271	50	3.96	2.81	0.71	29.8	10.6	1.20	.287	3.47	74	3.02	73	6.85	66.2
17	Héctor Neris H. Neris	11.12	627.1	643	46	43	.517	0	3.47	775	0	0	107	509	242	272	83	243	36	274	16	2,632	38	3.49	3.19	1.19	29.4	9.2	1.20	.285	3.90	84	3.75	89	7.30	33.5
18	Armando Benitez A. Benitez	10.93	779.0	762	40	47	.460	0	3.13	946	0	0	289	545	271	296	95	403	16	527	32	3,253	18	4.66	2.35	1.10	29.1	12.4	1.22	.251	3.42	72	3.86	88	6.30	48.8
19	Dylan Cease D. Cease	10.91	1015.1	188	65	58	.528	188	3.88	1,231	3	3	0	854	438	482	121	430	35	0	9	4,304	55	3.81	2.86	1.07	28.6	10.0	1.26	.295	4.27	93	3.66	85	7.57	67.6
20	Robbie Ray R. Ray	10.83	1441.0	265	88	81	.521	261	3.94	1,734	2	1	0	1,250	631	674	216	608	51	1	19	6,097	60	3.80	2.85	1.35	28.4	10.0	1.29	.296	4.21	94	4.06	99	7.81	5.1
21	Jacob deGrom J. deGrom	10.82	1539.2	248	96	65	.596	248	2.57	1,851	4	2	0	1,173	440	477	146	345	25	0	13	6,045	30	2.02	5.37	0.85	30.6	5.7	0.99	.279	2.79	66	2.70	66	6.86	239.4
22	Octavio Dotel O. Dotel	10.82	951.0	758	59	50	.541	34	3.78	1,143	0	0	109	765	399	431	117	412	41	305	39	4,024	46	3.90	2.77	1.11	28.4	10.2	1.24	.280	4.08	86	3.69	84	7.24	73.6
23	Andrew Miller A. Miller	10.63	829.0	612	55	55	.500	66	4.03	979	0	0	63	732	371	413	80	383	61	147	14	3,619	44	4.16	2.56	0.87	27.1	10.6	1.34	.308	4.48	95	3.63	87	7.95	49.8
24	Raisel Iglesias R. Iglesias	10.63	736.0	600	42	55	.433	21	2.92	869	0	0	253	570	239	265	83	202	27	459	17	2,962	17	2.47	4.30	1.01	29.3	6.8	1.05	.273	3.24	69	3.19	76	6.97	82.7
25	Randy Johnson R. Johnson	10.61	4135.1	618	303	166	.646	603	3.29	4,875	100	37	2	3,346	1,513	1,703	411	1,497	190	7	37	17,067	109	3.26	3.26	0.89	28.6	8.8	1.17	.291	3.71	75	3.18	73	7.28	554.3