In mountain oases of northern Oman, 107 different crop species were identified belonging to 39 families. Species number was highest among fruits (33 spp.), followed by vegetables (24 spp.). The number of species varied significantly between oases. Fruit species diversity and homogeneity of distribution of individual fruit species was highest at Balad Seet and lowest at Maqta as indicated by respective Shannon indices of 1.00 and 0.39 and evenness values of 32% and 16%. At Balad Seet and Maqta, date palm (Phoenix dactylifera L.) was the most common fruit crop with 2,690 and 2,128 specimens, respectively, while in the Al Jabal al Akhdar oasis system pomegranate (Punica granatum L.) was most frequent with 5,894 specimens. For date palm, 16 and 13 varieties were cultivated at Balad Seet and Maqta, with an average yield of 32 and 8 kg (palm yr)–1, respectively. Mean shoot circumference of date palm was significantly higher at Balad Seet compared to Maqta with 177 and 118 cm, respectively, indicating a lower palm vitality at Maqta. At Balad Seet 18 cultivated black mulberry (Morus nigra L.) trees were identified with a considerable tree-to-tree variation regarding fruit size. Average fruit length and diameter ranged from 11 to 79 mm and from 8 to 10 mm, respectively. Farmers did not distinguish, however, between different varieties. Temperate fruit and nut trees such as walnut (Juglans regia L.), apple (Malus domestica Borkh.), apricot (Prunus armeniaca L.), plum (Prunus domestica L.) and pear (Pyrus communis L.) were only cropped at the higher altitude sites of Al Jabal al Akhdar. Species similarity was greatest in Balad Seet and Al Jabal al Akhdar as indicated by a Sørensen coefficient of similarity of 67%. Overall this study shows a location-specific but surprisingly diverse mosaic of crops in Omani mountain oases which merits further studies and conservation efforts.