歐甘字母顯然是從一種基礎字母演變而成，有學者更指出它只是那種字母的密碼。大部分學者認為基礎字母是當時盛行的拉丁字母，也有人認為是古弗薩克文（Elder Futhark）或希臘字母。如果歐甘字母的起源是盧恩字母[5]，便能解釋在愛爾蘭語中沒有功能的字母 H 和 Z 存在的原因，以及拉丁文和希臘文中沒有的變異體字母 U 和 W ，但盧恩字母當時在歐洲大陸（Continental Europe）傳播不廣泛，作為基礎字母的可能性低於拉丁字母。
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Macalister, Robert A.S. Corpus inscriptionum insularum celticarum. First edition. Dublin: Stationery Office, 1945-1949. OCLC 71392234
McManus, Damian. Ogam: Archaizing, Orthography and the Authenticity of the Manuscript Key to the Alphabet, Ériu 37, 1988, 1-31. Dublin: Royal Irish Academy. OCLC 56088345
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MacNeill, Eoin. Archaisms in the Ogham Inscriptions, 'Proceedings of the Royal Irish Academy' 39, pp 33–53, Dublin
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Raftery, Barry. A Late Ogham Inscription from Co. Tipperary, Journal of the Royal Society of Antiquaries of Ireland 99, 1969. ISSN 0035-9106 OCLC 6906544
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Sims-Williams, Patrick. The Celtic Inscriptions of Britain: Phonology and Chronology, c. 400—1200. (Publications of the Philological Society 37) Oxford : Blackwell Publishing, 2003. ISBN 1-4051-0903-3
Thurneysen, Zum ogam Beiträge zur Geschichte der deutschen Sprache und Literatur, pp196–7, 1937
Vendryes L'écriture ogamique et ses origines Études Celtiques, 4, 1931, pp110– 113,
