The large petroleum reserve discovered offshore Kazakhstan in the northern portion of the Caspian Sea is estimated to range in size from 8 billion to more than 50 billion barrels of oil. If the 480 square mile deposit, to be known as the Kashagan field, proves to be nearer to the higher estimate in size, it could be the largest oil discovery in the past 20 years. The consortium which includes Exxon Mobil and Phillips Petroleum is very cautious at this stage because only one test well has been drilled so far in an area known as East Kashagan — the easternmost bulge of what is described as a dog bone-shaped field in shallow waters, stretching out deep underground. However, initial indications are extremely promising and that the bottom of the field has not yet been reached.