The Oakland Athletics have an ERA of 3.99 all-time.

	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	Athletics	2.94	1968	163	.506	82	80	163	997	45	15	30	1455.2	1,220	476	544	124	505	31	78	6,009	55	6.16	3.12	1.97	0.77	16.6	8.4	1.19	.252	3.36	7.54
2	Athletics	3.71	1969	162	.543	88	74	162	887	42	11	36	1480.2	1,356	611	678	163	586	39	48	6,244	55	5.39	3.56	1.51	0.99	14.2	9.4	1.31	.261	4.12	8.24
3	Athletics	3.30	1970	162	.549	89	73	162	858	33	11	40	1442.2	1,253	529	593	134	542	34	45	6,029	56	5.35	3.38	1.58	0.84	14.2	9.0	1.24	.251	3.70	7.82
4	Athletics	3.05	1971	161	.627	101	60	161	999	57	15	36	1469.1	1,229	498	564	131	501	33	57	6,018	37	6.12	3.07	1.99	0.80	16.6	8.3	1.18	.252	3.45	7.53
5	Athletics	2.58	1972	155	.600	93	62	155	862	42	15	43	1417.2	1,170	406	457	96	418	19	41	5,718	29	5.47	2.65	2.06	0.61	15.1	7.3	1.12	.248	2.90	7.43
6	Athletics	3.29	1973	162	.580	94	68	162	797	46	12	41	1457.1	1,311	532	615	143	494	30	27	6,048	52	4.92	3.05	1.61	0.88	13.2	8.2	1.24	.255	3.80	8.10
7	Athletics	2.95	1974	162	.556	90	72	162	755	49	11	28	1439.2	1,322	472	551	90	430	25	41	5,937	27	4.72	2.69	1.76	0.56	12.7	7.2	1.22	.266	3.44	8.26
8	Athletics	3.27	1975	162	.605	98	64	162	784	36	7	44	1448.0	1,267	526	606	102	523	37	41	6,039	47	4.87	3.25	1.50	0.63	13.0	8.7	1.24	.254	3.77	7.88
9	Athletics	3.26	1976	161	.540	87	74	161	711	39	13	29	1459.1	1,412	528	598	96	415	30	34	6,108	40	4.38	2.56	1.71	0.59	11.6	6.8	1.25	.271	3.69	8.71
10	Athletics	4.04	1977	161	.391	63	98	161	788	32	3	26	1436.2	1,459	645	749	145	560	24	49	6,201	55	4.94	3.51	1.41	0.91	12.7	9.0	1.41	.281	4.69	9.14
11	Athletics	3.62	1978	162	.426	69	93	162	750	26	6	29	1433.1	1,401	577	690	106	582	26	59	6,171	37	4.71	3.65	1.29	0.67	12.2	9.4	1.38	.275	4.33	8.80
12	Athletics	4.75	1979	162	.333	54	108	162	726	41	3	20	1429.1	1,606	754	860	147	654	49	67	6,436	72	4.57	4.12	1.11	0.93	11.3	10.2	1.58	.300	5.42	10.11
13	Athletics	3.46	1980	162	.512	83	79	162	769	94	8	13	1471.2	1,347	566	642	142	521	31	29	6,175	51	4.70	3.19	1.48	0.87	12.5	8.4	1.27	.256	3.93	8.24
14	Athletics	3.30	1981	109	.587	64	45	109	505	60	11	10	993.0	883	364	403	80	370	28	17	4,166	30	4.58	3.35	1.36	0.73	12.1	8.9	1.26	.252	3.65	8.00
15	Athletics	4.54	1982	162	.420	68	94	162	697	42	5	22	1456.0	1,506	735	819	177	648	30	21	6,430	58	4.31	4.01	1.08	1.09	10.8	10.1	1.48	.272	5.06	9.31
16	Athletics	4.34	1983	162	.457	74	88	162	719	22	7	33	1454.1	1,462	702	782	135	626	31	44	6,340	43	4.45	3.87	1.15	0.84	11.3	9.9	1.44	.275	4.84	9.05
17	Athletics	4.48	1984	162	.475	77	85	162	695	15	2	44	1430.0	1,554	712	796	155	592	35	34	6,315	47	4.37	3.73	1.17	0.98	11.0	9.4	1.50	.289	5.01	9.78
18	Athletics	4.41	1985	162	.475	77	85	162	785	10	1	41	1453.0	1,451	712	787	172	607	25	32	6,327	48	4.86	3.76	1.29	1.07	12.4	9.6	1.42	.270	4.87	8.99
19	Athletics	4.31	1986	162	.469	76	86	162	937	22	4	37	1433.0	1,334	686	760	166	667	34	35	6,208	62	5.88	4.19	1.40	1.04	15.1	10.7	1.40	.265	4.77	8.38
20	Athletics	4.32	1987	162	.500	81	81	162	1,042	18	2	40	1445.2	1,442	694	789	176	531	36	21	6,238	52	6.49	3.31	1.96	1.10	16.7	8.5	1.36	.284	4.91	8.98
21	Athletics	3.44	1988	162	.642	104	58	162	983	22	4	64	1489.1	1,376	569	620	116	553	29	27	6,256	62	5.94	3.34	1.78	0.70	15.7	8.8	1.30	.275	3.75	8.32
22	Athletics	3.09	1989	162	.611	99	63	162	930	17	3	57	1448.1	1,287	497	576	103	510	28	23	6,026	71	5.78	3.17	1.82	0.64	15.4	8.5	1.24	.266	3.58	8.00
23	Athletics	3.18	1990	162	.636	103	59	162	831	18	7	64	1456.0	1,287	514	570	123	494	27	19	6,020	50	5.14	3.05	1.68	0.76	13.8	8.2	1.22	.256	3.52	7.96
24	Athletics	4.57	1991	162	.519	84	78	162	892	14	3	49	1444.1	1,425	734	776	155	655	55	30	6,299	60	5.56	4.08	1.36	0.97	14.2	10.4	1.44	.280	4.84	8.88
25	Athletics	3.73	1992	162	.593	96	66	162	843	8	3	58	1447.0	1,396	599	672	129	601	41	46	6,204	67	5.24	3.74	1.40	0.80	13.6	9.7	1.38	.276	4.18	8.68
	Total	3.99		9,002	.513	4,614	4,387	9,002	54,708	1,027	249	2,157	80525.1	78,029	35,714	39,505	8,515	29,998	2,523	2,096	344,074	2,956	6.11	3.35	1.82	0.95	15.9	8.7	1.34	.280	4.42	8.72