{"cik":"0001473116","entityType":"other","sic":"","sicDescription":"","ownerOrg":"","insiderTransactionForOwnerExists":1,"insiderTransactionForIssuerExists":0,"name":"Yorktown Energy Partners VIII, L.P.","tickers":[],"exchanges":[],"ein":"262754039","lei":null,"description":"","website":"","investorWebsite":"","category":"","fiscalYearEnd":"1231","stateOfIncorporation":"DE","stateOfIncorporationDescription":"DE","addresses":{"mailing":{"street1":"410 PARK AVENUE","street2":"20TH FLOOR","city":"NEW YORK","stateOrCountry":"NY","zipCode":"10022","stateOrCountryDescription":"NY","isForeignLocation":0,"foreignStateTerritory":null,"country":null,"countryCode":null},"business":{"street1":"410 PARK AVENUE","street2":"20TH FLOOR","city":"NEW YORK","stateOrCountry":"NY","zipCode":"10022","stateOrCountryDescription":"NY","isForeignLocation":null,"foreignStateTerritory":null,"country":null,"countryCode":null}},"phone":"(212) 515-2100","flags":"","formerNames":[],"filings":{"recent":{"accessionNumber":["0001140361-26-005801","0001140361-25-042327","0001140361-25-031224","0001011438-25-000291","0001961863-25-000024","0001011438-25-000156","0001011438-24-000621","0001011438-24-000432","0001011438-24-000363","0001961863-24-000163","0001961863-24-000101","0001011438-24-000198","0001011438-23-000641","0001011438-23-000533","0001011438-23-000386","0001011438-23-000270","0001567619-22-020010","0000947871-22-000852","0000947871-22-000575","0000947871-22-000233","0000947871-21-001183","0001140361-21-034656","0000947871-21-000917","0001140361-21-026211","0000947871-21-000543","0001140361-21-006778","0000947871-21-000203","0000947871-20-000878","0001567619-20-015430","0001567619-20-010461","0001567619-20-004095","0001140361-19-020597","0001140361-19-020470","0000950123-19-008374","0000899243-19-014626","0000950123-19-005479","0001193125-19-080916","0000899243-19-007888","0000899243-19-007872","0000950123-19-002332","0001193125-18-342342","0000899243-18-028949","0000950123-18-011895","0000950123-18-008833","0000950123-18-005469","0000950123-18-002232","0000950123-17-010763","0000950123-17-007791","0000950123-17-005356","0000950123-17-002259","0000950123-16-022314","0000950123-16-020175","0000950123-16-017493","0000950123-16-015172","0000899243-15-010261","0001193125-14-226860","0001209191-14-021691","0001193125-14-097825","0001193125-12-433531","0001181431-12-055406","0001193125-11-356301","0001209191-11-062768","0000950123-09-046178","0001209191-09-045805"],"filingDate":["2026-02-17","2025-11-14","2025-08-14","2025-05-15","2025-02-18","2025-02-14","2024-11-13","2024-08-13","2024-05-15","2024-05-07","2024-03-12","2024-02-14","2023-11-14","2023-08-14","2023-05-12","2023-02-14","2022-11-14","2022-08-11","2022-05-16","2022-02-14","2021-11-15","2021-10-15","2021-08-16","2021-07-30","2021-05-17","2021-03-01","2021-02-16","2020-11-16","2020-08-14","2020-05-15","2020-02-14","2019-11-14","2019-11-13","2019-08-14","2019-05-23","2019-05-15","2019-03-20","2019-03-15","2019-03-15","2019-02-14","2018-12-04","2018-11-14","2018-11-14","2018-08-14","2018-05-15","2018-02-14","2017-11-14","2017-08-14","2017-05-15","2017-02-14","2016-11-14","2016-08-15","2016-05-16","2016-02-16","2015-12-21","2014-06-05","2014-03-19","2014-03-13","2012-10-24","2012-10-24","2011-12-30","2011-12-22","2009-09-25","2009-09-25"],"reportDate":["2025-12-31","2025-09-30","2025-06-30","2025-03-31","","2024-12-31","2024-09-30","2024-06-30","2024-03-31","","","2023-12-31","2023-09-30","2023-06-30","2023-03-31","2022-12-31","2022-09-30","2022-06-30","2022-03-31","2021-12-31","2021-09-30","2021-10-13","2021-06-30","2021-07-28","2021-03-31","2021-02-26","2020-12-31","2020-09-30","2020-06-30","2020-03-31","2019-12-31","2019-09-30","2019-11-12","2019-06-30","2019-05-21","2019-03-31","","2019-03-12","2019-03-12","2018-12-31","","2018-11-12","2018-09-30","2018-06-30","2018-03-31","2017-12-31","2017-09-30","2017-06-30","2017-03-31","2016-12-31","2016-09-30","2016-06-30","2016-03-31","2015-12-31","2015-12-09","","2014-03-10","","","2012-10-22","","2011-12-20","","2009-09-15"],"acceptanceDateTime":["2026-02-17T21:33:34.000Z","2025-11-14T21:19:55.000Z","2025-08-14T20:07:20.000Z","2025-05-15T15:39:22.000Z","2025-02-18T21:48:58.000Z","2025-02-14T16:55:03.000Z","2024-11-13T21:49:46.000Z","2024-08-13T18:47:37.000Z","2024-05-15T20:05:03.000Z","2024-05-07T20:22:12.000Z","2024-03-12T20:51:00.000Z","2024-02-14T14:36:29.000Z","2023-11-14T21:05:31.000Z","2023-08-14T20:03:39.000Z","2023-05-12T20:06:31.000Z","2023-02-14T14:56:09.000Z","2022-11-14T21:12:28.000Z","2022-08-11T10:09:58.000Z","2022-05-16T15:31:26.000Z","2022-02-14T21:28:14.000Z","2021-11-15T18:47:37.000Z","2021-10-15T23:28:32.000Z","2021-08-16T15:55:20.000Z","2021-07-30T18:01:11.000Z","2021-05-17T15:47:19.000Z","2021-03-02T02:45:53.000Z","2021-02-16T20:32:00.000Z","2020-11-16T20:32:16.000Z","2020-08-14T19:49:17.000Z","2020-05-15T19:39:51.000Z","2020-02-14T22:15:10.000Z","2019-11-14T21:17:16.000Z","2019-11-13T22:06:19.000Z","2019-08-14T20:19:45.000Z","2019-05-24T00:08:10.000Z","2019-05-15T20:30:53.000Z","2019-03-20T20:57:02.000Z","2019-03-15T10:37:38.000Z","2019-03-15T10:20:50.000Z","2019-02-14T22:01:30.000Z","2018-12-04T22:16:05.000Z","2018-11-14T23:23:41.000Z","2018-11-14T21:07:19.000Z","2018-08-14T19:48:37.000Z","2018-05-15T12:43:54.000Z","2018-02-14T18:25:38.000Z","2017-11-14T18:11:55.000Z","2017-08-14T16:33:31.000Z","2017-05-15T21:11:29.000Z","2017-02-14T18:42:30.000Z","2016-11-14T20:34:04.000Z","2016-08-15T20:29:47.000Z","2016-05-16T16:18:37.000Z","2016-02-16T22:29:58.000Z","2015-12-22T02:33:19.000Z","2014-06-05T18:15:29.000Z","2014-03-19T12:44:19.000Z","2014-03-13T20:37:00.000Z","2012-10-24T21:14:59.000Z","2012-10-24T15:38:42.000Z","2011-12-30T20:27:25.000Z","2011-12-22T18:07:41.000Z","2009-09-25T20:59:37.000Z","2009-09-25T20:41:21.000Z"],"act":["34","34","34","34","","34","34","34","34","","","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","34","","34","34","34","","34","34","34","34","34","34","34","34","34","34","34","34","34","34","","34","","","34","","34","","34"],"form":["13F-NT","13F-NT","13F-HR","13F-HR","144","13F-HR","13F-HR","13F-HR","13F-HR","144","144","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","4","13F-HR","4","13F-HR","3","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","4","13F-HR","4","13F-HR","SC 13D/A","4","3","13F-HR","SC 13D/A","4","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","3","SC 13D/A","4","SC 13D/A","SC 13D/A","4","SC 13D","3","SC 13D","3"],"fileNumber":["028-17371","028-17371","028-17371","028-17371","","028-17371","028-17371","028-17371","028-17371","","","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","001-15555","028-17371","001-15555","028-17371","001-15555","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","001-38075","028-17371","001-38075","028-17371","","001-38075","001-38075","028-17371","","001-34743","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","028-17371","001-32960","","001-35374","","","001-35374","","001-35374","","000-14731"],"filmNumber":["26642365","251486681","251218901","25950252","","25625305","241455243","241200702","24950285","","","24633166","231405902","231169668","23915645","23623722","221385392","221153513","22926765","22632818","211408822","211327060","211175850","211131716","21928729","21701065","21637165","201316255","201104741","20884574","20621899","191220450","191215077","191026691","19851799","19828750","","19682864","19682837","19607957","","181185471","181183690","181017043","18833277","18610399","171200085","171028652","17845699","17606579","161994328","161833183","161652052","161430535","151300646","","14702732","","","121157873","","111276766","","091087959"],"items":["","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","",""],"core_type":["13F-NT","13F-NT","13F-HR","13F-HR","144","13F-HR","13F-HR","13F-HR","13F-HR","144","144","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","4","13F-HR","4","13F-HR","3","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","4","13F-HR","4","13F-HR","SC 13D/A","4","3","13F-HR","SC 13D/A","4","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","13F-HR","3","SC 13D/A","4","SC 13D/A","SC 13D/A","4","SC 13D","3","SC 13D","3"],"size":[3609,3610,4869,5546,4607,5553,5555,5555,5557,6539,4607,5557,6103,6100,5515,5056,5353,5746,6244,6248,6249,26645,5745,25084,5743,23572,5755,5756,5357,5354,5356,5357,4772,6230,5096,6229,64836,7121,4797,6232,62584,5254,6236,6236,6235,6235,6236,6236,5665,5665,5666,5666,5666,5544,4628,63972,5003,62781,64002,4605,81255,3860,71700,18131],"isXBRL":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"isInlineXBRL":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"isXBRLNumeric":[null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null],"primaryDocument":["xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xsl144X01/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xsl144X01/primary_doc.xml","xsl144X01/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X02/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslF345X03/form4.xml","xslForm13F_X01/primary_doc.xml","xslF345X03/form4.xml","xslForm13F_X01/primary_doc.xml","xslF345X02/form3.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslF345X03/form4.xml","xslForm13F_X01/primary_doc.xml","xslF345X03/doc4.xml","xslForm13F_X01/primary_doc.xml","d710415dsc13da.htm","xslF345X03/doc4.xml","xslF345X02/doc3.xml","xslForm13F_X01/primary_doc.xml","d625232dsc13da.htm","xslF345X03/doc4.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslForm13F_X01/primary_doc.xml","xslF345X02/doc3.xml","d739231dsc13da.htm","xslF345X03/doc4.xml","d695029dsc13da.htm","d429632dsc13da.htm","xslF345X03/rrd358684.xml","d276261dsc13d.htm","xslF345X02/c26247_3x0.xml","c90546sc13d.htm","xslF345X02/c90547_3x1.xml"],"primaryDocDescription":["","","","","","","","","","","","","","","","","","","","","","","","FORM 4","","FORM 3","","","","","","","FORM 4","","FORM 4 SUBMISSION","","SC 13D/A","FORM 4 SUBMISSION","FORM 3 SUBMISSION","","SC 13D/A","FORM 4 SUBMISSION","","","","","","","","","","","","","FORM 3 SUBMISSION","SC 13D/A","FORM 4 SUBMISSION","SC 13D/A","SCHEDULE 13D AMENDMENT NO. 1","FORM 4","SCHEDULE 13D","MAIN DOCUMENT DESCRIPTION","SCHEDULE 13D","MAIN DOCUMENT DESCRIPTION"]},"files":[]}}