The oil fields of Burma occur as a long line from north to south near the center of the synclinal trough of Tertiary rocks which forms the central region of the country. The main fields are also puckers in the main trough. The region of Tertiary rocks is an old sea-gulf, bounded on the east by the Shan Plateau massif and on the west by the crestal rocks of the Arakan Yomas, which has gradually been filled up, mainly by river-borne sediments from the north. The oil appears to be found in the beds in which it was formed. The oil-bearing beds were laid down on the seaward side of the delta. Consequently the oil-bearing horizons follow the necessary conditions which, generally speaking, migrated gradually southward during the Tertiary period, though the southern course was in errupted at intervals. It is urged that a definite concentration of salts in the water is an essential condition for the formation of oil. Such a concentration may be attained either (a) on the seaward side of a delta, or (b) in a land-locked lagoon or lake. Probably the chemical nature of the salts varies greatly in different oil regions. A brief description of each of the fields is given and the change in the oil-bearing horizons illustrated by diagrammatic sections. The principal fields, from north to south, are Indaw, Yenangyat-Singu, Yenangyaung, Minbu (three small fields), Padaukpin, and Yenanma. The first and last two are comparatively recent discoveries. The largest producer has long been Yenangyaung which has yielded 3,000,000,000 gallons since 1900 from an area of a little more than one square mile. Singu has the largest reserves and is likely to take first place as a producer in the near future. All fields have been carefully and scientifically developed with the result that the total annual output of approximately 275,000,000 gallons during the past years will probably be maintained many years to come. The discovery of important new fields is unlikely.