Frank Thomas has the best career on-base percentage by a first baseman, with an on-base percentage of .452.

Interpreted as:

highest carrer obp with a minimum of 3000 PA by a first baseman

	NAME	OBP	PA	G	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	SB	CS	TB	XBH	SH	SF	IBB	GIDP	AVG	SLG	OPS	WRC	WRAA	WOBA	WRC+	BRAA
1	Frank Thomas F. Thomas	.452	4,089	918	3,262	681	1,083	215	6	225	745	741	25	470	17	13	1,985	446	0	61	105	103	.332	.609	1.061	897	403.1	.449	177	396
2	Lou Gehrig L. Gehrig	.447	9,660	2,164	8,001	1,888	2,721	534	163	493	1,995	1,508	45	790	102		5,060	1,190	106			2	.340	.632	1.080	2265	1,046.8	.477	173	980
3	Jimmie Foxx J. Foxx	.430	9,131	2,148	7,673	1,656	2,498	425	114	521	1,836	1,389	12	1,256	83		4,714	1,060	57			69	.326	.614	1.044	2036	900.3	.463	159	752
4	Dan Brouthers D. Brouthers	.426	7,388	1,608	6,441	1,463	2,210	442	196	98	994	822	105	83	256		3,338	736	20				.343	.518	.944	1810	703.6	.437	155	632.9
5	Ferris Fain F. Fain	.424	4,904	1,151	3,930	595	1,139	213	30	48	570	904	18	261	46	12	1,556	291	44	8	3	117	.290	.396	.820	777	203	.390	127	161
6	Todd Helton T. Helton	.415	9,349	2,212	7,869	1,388	2,493	590	36	364	1,395	1,327	57	1,164	37	28	4,247	990	3	93	185	185	.317	.540	.955	1750	610.4	.406	132	390.6
7	Stan Musial S. Musial	.411	4,894	1,145	4,237	709	1,388	270	58	183	732	593	24	254	24	7	2,323	511	14	26	90	111	.328	.548	.959	915	356.5	.423	151	304.9
8	Jim Thome J. Thome	.410	5,292	1,238	4,272	836	1,190	229	12	337	909	947	32	1,338	4	9	2,454	578	0	41	107	64	.279	.574	.984	1026	365.8	.414	150	336.9
9	Hank Greenberg H. Greenberg	.410	5,030	1,148	4,282	859	1,331	304	60	275	1,052	701	15	717	48		2,580	639	32			41	.311	.603	1.012	1054	447.6	.451	152	358.3
10	Joey Votto J. Votto	.409	8,746	2,056	7,252	1,171	2,135	459	22	356	1,144	1,365	81	1,640	80	29	3,706	837	0	48	147	168	.294	.511	.920	1563	539.6	.394	145	472.9
11	Jason Giambi J. Giambi	.409	6,942	1,745	5,626	987	1,598	314	7	352	1,147	1,101	142	1,212	15	9	2,982	673	1	72	78	129	.284	.530	.939	1284	425.9	.403	145	401.8
12	Jeff Bagwell J. Bagwell	.408	9,431	2,150	7,797	1,517	2,314	488	32	449	1,529	1,401	128	1,558	202	78	4,213	969	3	102	155	221	.297	.540	.948	1755	596.6	.405	149	588.3
13	Lu Blue L. Blue	.402	7,207	1,615	5,904	1,152	1,696	319	109	44	695	1,092	43	436	151		2,365	472	168				.287	.401	.803	1102	191.5	.380	112	118
14	Rod Carew R. Carew	.402	5,602	1,297	4,865	784	1,595	233	60	46	542	619	10	481	181	106	2,086	339	71	37	93	108	.328	.429	.831	853	228.8	.372	132	208.5
15	Nick Johnson N. Johnson	.402	3,116	770	2,539	409	693	165	5	89	379	487	68	523	27	23	1,135	259	9	13	42	72	.273	.447	.849	497	117	.373	128	109.7
16	Carl Yastrzemski C. Yastrzemski	.401	3,252	765	2,710	462	793	132	9	109	438	504	7	306	57	37	1,270	250	2	29	59	69	.293	.469	.870	533	177.9	.391	139	145.2
17	Lance Berkman L. Berkman	.401	3,684	886	3,064	513	882	194	10	173	571	570	26	613	44	16	1,615	377	0	24	87	87	.288	.527	.928	650	204.7	.394	141	190.9
18	Roger Connor R. Connor	.401	7,979	1,799	6,980	1,469	2,203	395	221	131	1,071	951	39	151	244		3,433	747	9				.316	.492	.892	1773	571.8	.414	142	519.1
19	John Kruk J. Kruk	.401	3,167	779	2,660	431	799	138	18	79	420	465	2	487	43	21	1,210	235	6	34	65	55	.300	.455	.855	505	138.6	.377	136	134.3
20	John Olerud J. Olerud	.400	8,642	2,123	7,234	1,096	2,144	485	12	241	1,182	1,218	87	941	11	12	3,376	738	11	92	151	227	.296	.467	.866	1407	344.6	.378	130	332.5
21	Frank Chance F. Chance	.399	4,258	1,046	3,570	665	1,067	169	67	18	511	490	103	261	351		1,424	254	95				.299	.399	.798	674	232.5	.390	141	200.1
22	Cap Anson C. Anson	.398	9,264	2,092	8,279	1,552	2,727	489	114	95	1,306	919	32	146	247		3,729	698	34				.329	.450	.849	1973	596.5	.399	134	475.5
23	Johnny Mize J. Mize	.397	7,371	1,884	6,443	1,118	2,011	367	83	359	1,337	856	52	524	28	0	3,621	809	20			76	.312	.562	.959	1421	546.3	.433	157	508.1
24	Mark McGwire M. McGwire	.395	7,602	1,856	6,134	1,157	1,616	251	6	580	1,405	1,313	74	1,578	12	7	3,619	837	3	78	150	147	.263	.590	.985	1475	566.5	.416	158	559.7
25	Mike Hargrove M. Hargrove	.395	5,520	1,369	4,582	626	1,323	218	22	59	560	798	44	429	18	29	1,762	299	40	56	60	129	.289	.385	.780	774	163.3	.357	123	140.3