Between the 1978 and 1987 seasons, the Seattle Mariners had the worst winning percentage by a team, winning 41.9 percent of the time.

	TEAM	W%	W	L	G	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	SB	CS	PA	TB	XBH	SH	SF	IBB	GIDP	AVG	OBP	SLG	OPS
1	Mariners	.419	655	910	1,567	53,206	6,449	13,567	2,390	362	1,282	6,086	4,920	292	8,177	1,217	619	59,373	20,527	4,034	542	413	328	1,207	.255	.319	.386	.705
2	Indians	.456	709	846	1,557	53,231	7,018	14,195	2,287	343	1,150	6,549	5,398	279	7,357	1,243	644	60,000	20,618	3,780	565	527	346	1,299	.267	.334	.387	.722
3	Twins	.458	717	849	1,567	53,460	6,749	14,052	2,484	408	1,276	6,370	4,745	279	7,655	644	436	59,534	21,180	4,168	586	464	365	1,306	.263	.324	.396	.720
4	Athletics	.461	723	844	1,567	52,789	6,680	13,339	2,130	300	1,394	6,250	5,091	237	8,613	1,529	746	59,241	20,251	3,824	639	485	332	1,121	.253	.319	.384	.702
5	Cubs	.465	724	832	1,560	53,301	6,579	13,772	2,355	378	1,263	6,161	4,924	224	8,702	1,141	550	59,558	20,672	3,996	668	441	565	1,101	.258	.321	.388	.709
6	Braves	.468	730	829	1,560	52,586	6,405	13,286	2,190	281	1,260	5,972	5,218	238	8,330	1,096	652	59,145	19,818	3,731	716	387	593	1,214	.253	.321	.377	.698
7	Rangers	.472	737	823	1,563	53,258	6,746	14,037	2,307	311	1,293	6,344	4,777	282	7,683	1,028	619	59,304	20,845	3,911	523	464	373	1,262	.264	.325	.391	.716
8	Padres	.474	742	825	1,569	53,187	6,155	13,548	2,086	402	908	5,690	4,901	233	8,161	1,424	673	59,573	19,162	3,396	852	400	722	1,114	.255	.318	.360	.678
9	Blue Jays	.482	753	809	1,564	53,598	6,765	13,999	2,504	446	1,350	6,333	4,567	325	7,677	1,058	643	59,341	21,445	4,300	443	408	351	1,140	.261	.321	.400	.721
10	Giants	.483	758	810	1,568	52,940	6,364	13,241	2,200	325	1,206	5,930	5,318	240	9,150	1,185	690	59,699	19,709	3,731	804	397	635	1,121	.250	.319	.372	.691
11	Mets	.486	758	803	1,564	53,095	6,296	13,467	2,257	341	1,068	5,867	5,013	255	8,978	1,317	623	59,489	19,610	3,666	674	452	616	1,151	.254	.319	.369	.688
12	Pirates	.487	759	799	1,560	53,270	6,484	13,897	2,481	382	1,109	6,074	4,693	243	8,244	1,507	726	59,452	20,469	3,972	764	482	681	1,127	.261	.321	.384	.705
13	White Sox	.489	762	797	1,562	52,901	6,820	13,788	2,389	378	1,305	6,415	4,612	373	7,872	1,105	547	58,918	20,848	4,072	543	489	353	1,203	.261	.322	.394	.716
14	Angels	.506	792	774	1,566	53,240	7,251	13,871	2,266	290	1,457	6,776	5,647	374	8,196	837	498	60,512	21,088	4,013	780	471	390	1,313	.261	.333	.396	.729
15	Reds	.512	801	762	1,565	52,859	6,599	13,498	2,432	329	1,190	6,154	5,462	210	8,711	1,400	563	59,682	20,158	3,951	702	449	614	1,209	.255	.325	.381	.706
16	Astros	.519	814	755	1,569	53,109	6,132	13,643	2,286	476	857	5,737	4,760	191	7,992	1,473	665	59,283	19,452	3,619	766	457	652	1,040	.257	.318	.366	.684
17	Cardinals	.525	818	741	1,561	53,077	6,695	13,891	2,439	516	794	6,233	5,136	219	8,126	1,869	707	59,646	19,744	3,749	726	488	611	1,117	.262	.327	.372	.699
18	Expos	.525	820	741	1,562	53,122	6,449	13,652	2,554	415	1,138	6,025	4,755	290	8,279	1,529	604	59,268	20,450	4,107	676	425	680	1,091	.257	.319	.385	.704
19	Brewers	.527	824	739	1,564	53,986	7,430	14,611	2,594	397	1,492	7,043	4,805	255	7,580	947	514	60,132	22,475	4,483	583	503	407	1,169	.271	.330	.416	.747
20	Phillies	.527	825	739	1,566	53,130	6,798	13,758	2,389	422	1,286	6,361	5,402	304	8,949	1,366	612	59,926	20,849	4,097	624	466	634	1,177	.259	.328	.392	.721
21	Dodgers	.528	828	741	1,570	53,217	6,459	13,681	2,139	249	1,332	6,093	5,008	244	8,341	1,284	601	59,790	20,314	3,720	903	418	625	1,110	.257	.322	.382	.703
22	Royals	.530	827	734	1,562	53,731	7,009	14,485	2,627	524	1,207	6,623	4,544	294	7,552	1,479	552	59,449	21,781	4,358	381	499	425	1,184	.270	.327	.405	.733
23	Red Sox	.537	839	723	1,563	54,186	7,636	15,003	2,747	319	1,557	7,229	5,293	331	7,467	539	369	60,777	23,059	4,623	468	499	409	1,467	.277	.342	.426	.768
24	Orioles	.546	851	707	1,559	53,070	7,159	13,861	2,381	215	1,680	6,774	5,697	231	8,120	689	411	59,832	21,712	4,276	394	440	386	1,395	.261	.333	.409	.742
25	Tigers	.551	863	702	1,566	53,786	7,511	14,374	2,355	397	1,646	7,080	5,559	319	8,156	1,013	565	60,650	22,461	4,398	494	492	380	1,139	.267	.337	.418	.754