Lead isotope data, together with an evaluation of previously published results for the chemical composition of Omani ores and copper-base artefacts are used to define a material signature of Omani copper. Absent from our group of Bronze Age metal (Umm an Nar and Wadi Suq periods) are the signature of ores from Masirah Island and also from the vast deposits in north Oman inland from Suhar. Contemporaneous copper from Bahrain and from Tell Abraq on the Gulf coast is consistent in its material signature with Omani copper; a derivation from Omani ores of this copper is highly likely. A few exceptions at Tell Abraq point to Faynan/Timna in the southern Levant as a possible source region. Among Mesopotamian artefacts the signature of Omani copper is encountered during all cultural periods from Uruk at the end of the fourth millennium BC to Akkadian 1000 years later. Oman/Magan appears to have been particularly important during Early Dynastic III and Akkadian when about half of the copper in circulation bears the Omani signature.