Abstract All of Myanmar’s commercial onshore oil- and gas fields occur in Cenozoic sedimentary rocks in the Central Burma Depression. The state oil company, Myanmar Oil and Gas Enterprise (MOGE), and most observers divide this very large Cenozoic downwarp into at least seven basins (Fig. 4.1), which is the scheme adopted here for descriptive purposes; others prefer to refer to these seven basins as sub-basins. They can be grouped under two main headings: a northern pair of basins (Chindwin and Shwebo-Monywa basins) in which a few discoveries have been made (in the former) but from which there is no commercial production at present; and a southern region which contains all of the currently producing fields. The boundary between southern and northern regions is at about the latitude of Mandalay, c. 22°N (Fig. 4.1), where there is a slight east–­west structural arch which marks the southern boundary of the Chindwin and Shwebo-Monywa basins. An alternative classification is along plate-tectonic lines, the forearc domain comprising the Chindwin, Salin, Pyay and less certainly the Hukawng basins, and the back-arc domain comprising the Shwebo-Monywa, Bago Yoma and Sittaung basins. The drawbacks of this scheme are that: (1) it is not clear into which domain the Hukawng Basin should be placed; and (2) the Ayeyarwady Delta Basin straddles the buried magmatic arc and so is in both the forearc and back-arc domains. Because of the contentious plate-tectonic categorization of the Hukawng Basin and its frontier exploration status, we have chosen to describe it separately (in Chapter 5) from the basins which lie clearly in the Central Burma Depression.