The Philadelphia Phillies have the highest ERA by a team in a season, with an ERA of 6.71 in 1930.

	TEAM	ERA	SEASON	G	W%	W	L	GS	SO	CG	SHO	SV	IP	H	ER	R	HR	BB	HBP	IBB	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	H/9
1	Phillies	6.71	1930	156	.338	52	102	156	384	54	3	7	1372.2	1,993	1,024	1,199	142	543	33		6,549	23	2.52	3.56	0.71	0.93	5.9	8.3	1.85	.340	7.86	13.07
2	Tigers	6.38	1996	162	.327	53	109	162	957	10	4	22	1432.2	1,699	1,015	1,103	241	784	80	63	6,713	82	6.01	4.93	1.22	1.51	14.3	11.7	1.73	.313	6.93	10.67
3	Spiders	6.37	1899	154	.130	20	134	154	215	138		0	1264.0	1,844	894	1,252	43	527	109		6,076	40	1.53	3.75	0.41	0.31	3.5	8.7	1.88	.348	8.91	13.13
4	Browns	6.24	1936	155	.375	57	95	155	399	54	3	13	1348.1	1,776	935	1,064	115	609	47		6,382	44	2.66	4.07	0.66	0.77	6.3	9.5	1.77	.319	7.10	11.85
5	Browns	6.17	1897	133	.221	29	102	133	207	110		1	1136.1	1,594	779	1,088	54	454	71		5,380	40	1.64	3.60	0.46	0.43	3.8	8.4	1.80	.335	8.62	12.62
6	Phillies	6.13	1929	154	.464	71	82	154	369	45	5	24	1348.0	1,743	918	1,036	122	616	39		6,303	21	2.46	4.11	0.60	0.81	5.9	9.8	1.75	.314	6.92	11.64
7	Bisons	6.11	1890	134	.273	36	96	134	351	125		0	1141.0	1,499	775	1,199	67	673	48		5,658	78	2.77	5.31	0.52	0.53	6.2	11.9	1.90	.317	9.46	11.82
8	Athletics	6.08	1936	154	.346	53	100	154	405	68	3	11	1352.1	1,645	913	1,045	131	696	24		6,301	67	2.70	4.63	0.58	0.87	6.4	11.0	1.73	.300	6.95	10.95
9	Rockies	6.01	1999	162	.444	72	90	162	1,032	12	1	33	1429.0	1,700	955	1,028	237	737	60	46	6,574	70	6.50	4.64	1.40	1.49	15.7	11.2	1.71	.325	6.47	10.71
10	Browns	6.01	1939	156	.279	43	111	156	516	56	3	4	1371.1	1,724	916	1,035	133	739	29		6,474	32	3.39	4.85	0.70	0.87	8.0	11.4	1.80	.315	6.79	11.31
11	Browns	6.00	1937	156	.299	46	108	156	468	55	2	8	1363.0	1,770	909	1,023	143	653	30		6,371	34	3.09	4.31	0.72	0.94	7.3	10.2	1.78	.320	6.75	11.69
12	Reds	5.99	1894	134	.423	55	75	134	223	112		3	1165.1	1,615	775	1,108	85	500	56		5,528	35	1.72	3.86	0.45	0.66	4.0	9.0	1.81	.328	8.56	12.47
13	Alleghenys	5.97	1890	138	.169	23	113	138	381	119		0	1176.1	1,520	780	1,235	52	573	79		5,664	115	2.91	4.38	0.66	0.40	6.7	10.1	1.78	.321	9.45	11.63
14	Colonels	5.90	1893	126	.400	50	75	126	190	113		1	1080.0	1,431	708	942	38	479	49		5,156	29	1.58	3.99	0.40	0.32	3.7	9.3	1.77	.317	7.85	11.93
15	Colonels	5.90	1895	133	.267	35	96	133	245	104		1	1117.1	1,520	732	1,090	40	469	63		5,290	48	1.97	3.78	0.52	0.32	4.6	8.9	1.78	.331	8.78	12.24
16	Orioles	5.84	2021	162	.321	52	110	162	1,234	1	1	26	1402.0	1,518	910	956	258	563	68	12	6,252	88	7.92	3.61	2.19	1.66	19.7	9.0	1.48	.305	6.14	9.74
17	Browns	5.80	1938	156	.362	55	97	156	632	71	3	7	1344.2	1,584	867	962	132	737	26		6,222	27	4.23	4.93	0.86	0.88	10.2	11.8	1.73	.309	6.44	10.60
18	Athletics	5.79	1939	153	.362	55	97	153	397	50	6	12	1342.2	1,687	864	1,022	148	579	19		6,248	35	2.66	3.88	0.69	0.99	6.4	9.3	1.69	.301	6.85	11.31
19	Twins	5.76	1995	144	.389	56	88	144	790	7	2	27	1272.2	1,450	815	889	210	533	36	18	5,714	52	5.59	3.77	1.48	1.49	13.8	9.3	1.56	.299	6.29	10.25
20	Browns	5.73	1895	136	.298	39	92	136	284	106		1	1161.1	1,572	739	1,036	64	443	48		5,430	20	2.20	3.43	0.64	0.50	5.2	8.2	1.74	.328	8.03	12.18
21	Colts	5.72	1894	137	.432	57	75	137	284	118		0	1163.0	1,575	739	1,080	43	569	64		5,556	38	2.20	4.40	0.50	0.33	5.1	10.2	1.84	.333	8.36	12.19
22	Rangers	5.71	2001	162	.451	73	89	162	951	4	1	37	1438.1	1,670	913	968	222	596	63	33	6,469	70	5.95	3.73	1.60	1.39	14.7	9.2	1.58	.312	6.06	10.45
23	Twins	5.68	1994	113	.469	53	60	113	602	6	2	29	1005.0	1,197	634	688	153	388	31	20	4,507	43	5.39	3.47	1.55	1.37	13.4	8.6	1.58	.313	6.16	10.72
24	Rockies	5.67	2023	162	.364	59	103	162	1,129	0	0	31	1414.0	1,599	891	957	234	586	86	13	6,316	51	7.19	3.73	1.93	1.49	17.9	9.3	1.55	.319	6.09	10.18
25	Rangers	5.67	2003	162	.438	71	91	162	1,009	4	2	43	1433.1	1,625	903	969	208	603	63	45	6,413	51	6.34	3.79	1.67	1.31	15.7	9.4	1.55	.313	6.08	10.20