Since 1947, the Colorado Rockies have the highest ERA by an NL team in a season, with an ERA of 6.01 in 1999.

	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	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
2	Rockies	5.98	2025	157	.274	43	114	157	1,062	0	0	29	1367.1	1,631	908	992	240	534	69	18	6,183	59	6.99	3.51	1.99	1.58	17.2	8.6	1.58	.325	6.53	10.74
3	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
4	Rockies	5.59	1996	162	.512	83	79	162	932	5	1	34	1422.2	1,597	884	964	198	624	69	19	6,391	66	5.90	3.95	1.49	1.25	14.6	9.8	1.56	.306	6.10	10.10
5	Rockies	5.59	2020	60	.433	26	34	60	393	1	0	16	526.1	579	327	353	83	205	40	5	2,335	29	6.72	3.51	1.92	1.42	16.8	8.8	1.49	.307	6.04	9.90
6	Rockies	5.56	2019	162	.438	71	91	162	1,264	1	1	28	1448.2	1,576	895	958	270	589	57	33	6,423	63	7.85	3.66	2.15	1.68	19.7	9.2	1.49	.308	5.95	9.79
7	Rockies	5.54	2004	162	.420	68	94	162	947	3	0	36	1435.1	1,634	883	923	198	697	71	84	6,535	66	5.94	4.37	1.36	1.24	14.5	10.7	1.62	.311	5.79	10.25
8	Rockies	5.47	2024	162	.377	61	101	162	1,118	0	0	37	1426.2	1,604	867	929	221	563	66	12	6,322	59	7.05	3.55	1.99	1.39	17.7	8.9	1.52	.318	5.86	10.12
9	Astros	5.42	2000	162	.444	72	90	162	1,064	8	1	30	1437.2	1,596	865	944	234	598	60	25	6,455	55	6.66	3.74	1.78	1.46	16.5	9.3	1.53	.303	5.91	9.99
10	Rockies	5.41	1993	162	.414	67	95	162	913	9	0	35	1431.1	1,664	860	967	181	609	41	66	6,471	82	5.74	3.83	1.50	1.14	14.1	9.4	1.59	.314	6.08	10.46
11	Nationals	5.34	2025	159	.409	65	94	159	1,218	0	0	36	1396.1	1,459	828	876	207	560	88	6	6,168	67	7.85	3.61	2.17	1.33	19.7	9.1	1.45	.306	5.65	9.40
12	Rockies	5.29	2001	162	.451	73	89	162	1,058	8	4	26	1430.0	1,522	841	906	239	598	64	71	6,306	38	6.66	3.76	1.77	1.50	16.8	9.5	1.48	.295	5.70	9.58
13	Cubs	5.27	1999	162	.414	67	95	162	980	11	3	32	1430.2	1,619	837	920	221	529	27	48	6,359	59	6.16	3.33	1.85	1.39	15.4	8.3	1.50	.304	5.79	10.18
14	Rockies	5.26	2000	162	.506	82	80	162	1,001	7	1	33	1430.0	1,568	835	897	221	588	72	72	6,340	40	6.30	3.70	1.70	1.39	15.8	9.3	1.51	.302	5.65	9.87
15	Cubs	5.25	2000	162	.401	65	97	162	1,143	10	1	39	1454.2	1,505	849	904	231	658	62	45	6,451	45	7.07	4.07	1.74	1.43	17.7	10.2	1.49	.292	5.59	9.31
16	Rockies	5.25	1997	162	.512	83	79	162	870	9	3	38	1432.2	1,697	836	908	196	566	67	23	6,417	50	5.47	3.56	1.54	1.23	13.6	8.8	1.58	.318	5.70	10.66
17	Pirates	5.22	1953	154	.325	50	104	154	607	49	4	10	1358.0	1,529	788	887	168	577	21		6,059	44	4.02	3.82	1.05	1.11	10.0	9.5	1.55	.290	5.88	10.13
18	Rockies	5.22	2012	162	.395	64	98	162	1,144	0	0	36	1422.0	1,637	824	890	198	566	47	61	6,384	94	7.24	3.58	2.02	1.25	17.9	8.9	1.55	.325	5.63	10.36
19	Rockies	5.20	2002	162	.451	73	89	162	920	1	0	43	1426.2	1,554	825	898	225	582	64	49	6,345	42	5.80	3.67	1.58	1.42	14.5	9.2	1.50	.292	5.66	9.80
20	Rockies	5.20	2003	162	.457	74	88	162	866	3	0	34	1420.0	1,629	821	892	200	552	84	51	6,364	48	5.49	3.50	1.57	1.27	13.6	8.7	1.54	.307	5.65	10.32
21	Reds	5.19	2004	162	.469	76	86	162	992	5	2	47	1443.2	1,595	832	907	236	572	54	55	6,451	74	6.18	3.57	1.73	1.47	15.4	8.9	1.50	.296	5.65	9.94
22	Pirates	5.18	2019	162	.426	69	93	162	1,443	1	0	31	1440.0	1,511	829	911	241	584	85	22	6,391	50	9.02	3.65	2.47	1.51	22.6	9.1	1.45	.315	5.69	9.44
23	Marlins	5.18	1998	162	.333	54	108	162	1,016	11	0	24	1449.2	1,617	834	923	182	715	58	61	6,553	62	6.31	4.44	1.42	1.13	15.5	10.9	1.61	.313	5.73	10.04
24	Reds	5.17	2017	162	.420	68	94	162	1,300	2	1	33	1430.0	1,442	821	869	248	631	77	37	6,286	62	8.18	3.97	2.06	1.56	20.7	10.0	1.45	.296	5.47	9.08
25	Rockies	5.15	1994	117	.453	53	64	117	703	4	1	28	1031.0	1,185	590	638	120	448	49	43	4,644	50	6.14	3.91	1.57	1.05	15.1	9.6	1.58	.320	5.57	10.34