Between the 1900 and 1946 seasons, the Baltimore Orioles had the worst ERA by a team, with an ERA of 4.04.

	TEAM	ERA	G	W%	W	L	GS	SO	CG	SHO	SV	IP	H	ER	R	HR	BB	HBP	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	H/9
1	Orioles	4.04	276	.435	118	153	276	529	234	7	4	2368.1	2,844	1,062	1,598	51	698	85	10,397	55	2.01	2.65	0.76	0.19	5.1	6.7	1.50	.309	6.07	10.81
2	Phillies	4.02	7,126	.424	2,993	4,072	7,126	22,170	3,651	442	438	63274.1	68,841	28,246	35,055	2,902	22,051	1,864	274,390	1,347	3.15	3.14	1.01	0.41	8.1	8.0	1.44	.293	4.99	9.79
3	Browns	3.93	7,033	.441	3,063	3,876	7,033	22,266	3,746	411	407	62479.0	65,939	27,295	33,731	2,848	23,210	1,645	268,575	1,203	3.21	3.34	0.96	0.41	8.3	8.6	1.43	.289	4.86	9.50
4	Athletics	3.81	6,973	.483	3,332	3,570	6,973	25,478	3,773	471	452	61958.2	63,119	26,196	32,480	2,674	23,793	1,636	265,050	1,493	3.70	3.46	1.07	0.39	9.6	9.0	1.40	.286	4.72	9.17
5	Braves	3.66	7,157	.428	3,023	4,048	7,157	21,097	4,013	479	347	63866.2	66,519	25,994	32,359	2,537	21,269	1,549	271,722	1,183	2.97	3.00	0.99	0.36	7.8	7.8	1.37	.284	4.56	9.37
6	Tigers	3.66	7,029	.522	3,635	3,323	7,029	24,191	3,921	461	525	62704.1	64,295	25,506	32,005	2,327	23,166	1,860	268,262	1,205	3.47	3.33	1.04	0.33	9.0	8.6	1.39	.286	4.59	9.23
7	Senators	3.65	7,026	.482	3,340	3,594	7,026	24,536	3,840	479	529	62570.1	63,732	25,370	31,702	2,102	22,314	1,644	266,323	1,477	3.53	3.21	1.10	0.30	9.2	8.4	1.38	.286	4.56	9.17
8	Red Sox	3.61	7,006	.494	3,427	3,506	7,006	23,518	3,849	479	434	62453.2	63,309	25,055	30,866	2,246	21,635	1,520	264,672	1,162	3.39	3.12	1.09	0.32	8.9	8.2	1.36	.283	4.45	9.12
9	Indians	3.54	7,028	.515	3,583	3,370	7,028	23,857	3,924	511	468	62570.0	63,959	24,605	30,889	1,901	22,345	1,576	265,808	1,277	3.43	3.21	1.07	0.27	9.0	8.4	1.38	.287	4.44	9.20
10	Terrapins	3.54	314	.425	131	177	314	1,302	173	20	20	2752.1	2,844	1,082	1,388	86	858	78	11,244	61	4.26	2.81	1.52	0.28	11.6	7.6	1.35	.309	4.54	9.30
11	Cardinals	3.49	7,178	.509	3,613	3,483	7,178	24,202	3,897	476	529	64094.1	65,326	24,866	31,251	2,472	20,955	1,666	272,125	1,274	3.40	2.94	1.15	0.35	8.9	7.7	1.35	.282	4.39	9.17
12	White Sox	3.49	7,006	.501	3,474	3,456	7,006	23,040	3,948	539	462	62736.1	63,161	24,307	30,102	2,414	20,318	1,358	264,199	1,172	3.31	2.91	1.13	0.35	8.7	7.7	1.33	.280	4.32	9.06
13	Dodgers	3.47	7,158	.489	3,463	3,616	7,158	25,102	3,955	521	494	63905.2	64,223	24,614	30,963	2,406	21,404	1,724	270,903	1,205	3.54	3.01	1.17	0.34	9.3	7.9	1.34	.281	4.36	9.04
14	Yankees	3.44	6,723	.566	3,765	2,889	6,723	24,968	3,772	471	549	60050.1	58,952	22,952	28,299	2,453	20,831	1,326	252,431	1,137	3.74	3.12	1.20	0.37	9.9	8.3	1.33	.279	4.24	8.84
15	Tip-Tops	3.35	310	.480	147	159	310	1,103	169	20	25	2741.0	2,674	1,020	1,350	58	1,095	76	11,416	70	3.62	3.60	1.01	0.19	9.7	9.6	1.38	.288	4.43	8.78
16	Reds	3.33	7,189	.486	3,452	3,656	7,189	22,069	4,117	509	420	64102.0	64,799	23,696	30,160	1,913	19,536	1,619	269,557	1,031	3.10	2.74	1.13	0.27	8.2	7.2	1.32	.280	4.23	9.10
17	Pirates	3.28	7,170	.550	3,903	3,193	7,170	22,265	4,022	569	458	64010.0	64,051	23,322	29,063	2,097	18,215	1,553	268,368	1,004	3.13	2.56	1.22	0.29	8.3	6.8	1.29	.276	4.09	9.01
18	Giants	3.28	7,160	.560	3,962	3,116	7,160	25,276	3,736	536	679	63868.2	63,425	23,268	28,892	2,901	18,838	1,313	268,071	1,282	3.56	2.65	1.34	0.41	9.4	7.0	1.29	.275	4.07	8.94
19	Blues	3.27	308	.508	154	149	308	1,256	168	25	27	2747.0	2,520	998	1,236	80	1,058	76	11,249	65	4.12	3.47	1.19	0.26	11.2	9.4	1.30	.278	4.05	8.26
20	Cubs	3.20	7,188	.554	3,943	3,168	7,188	25,786	4,113	635	484	64407.2	63,159	22,874	28,632	2,311	20,368	1,546	270,442	1,225	3.60	2.85	1.27	0.32	9.5	7.5	1.30	.276	4.00	8.83
21	Rebels	3.18	310	.495	150	153	310	1,027	185	25	18	2752.1	2,689	971	1,222	74	885	53	11,152	44	3.36	2.89	1.16	0.24	9.2	7.9	1.30	.287	4.00	8.79
22	Terriers	3.15	313	.489	149	156	313	1,359	191	33	15	2793.2	2,685	978	1,225	60	805	71	11,396	60	4.38	2.59	1.69	0.19	11.9	7.1	1.25	.288	3.95	8.65
23	Packers	3.11	307	.487	148	156	307	1,126	177	25	23	2720.0	2,597	941	1,234	66	835	83	11,102	74	3.73	2.76	1.35	0.22	10.1	7.5	1.26	.281	4.08	8.59
24	Peppers	2.83	312	.551	168	137	312	1,245	204	31	16	2804.1	2,660	882	1,184	44	929	102	11,450	63	4.00	2.98	1.34	0.14	10.9	8.1	1.28	.287	3.80	8.54
25	Whales	2.54	312	.565	173	133	312	1,226	190	35	18	2818.0	2,436	795	1,055	77	795	66	11,176	59	3.92	2.54	1.54	0.25	11.0	7.1	1.15	.262	3.37	7.78