It naturally follows that, with the constant withdrawal of large supplies of crude oil from Mother Earth, Nature’s stores must be growing less, and it is not surprising, therefore, to hear, with persistent regularity, alarming rumours of the coming dearth of crude oil. Experts have devoted considerable time and thought in an endeavour to arrive at a conclusion as to the length of time it will take for the withdrawal of practically the whole of the crude oil from the known deposits in the more developed fields: their conclusions, however, are widely different, for while some assert that in the United States, for instance, the known fields will cease to be commercially productive within forty years, others there are who declare that centuries must elapse before the question of a failing supply need call for serious consideration. But there is one point which must not be overlooked in this connection, and that is the fact that, while thus far very few thoroughly developed oil-fields have shown signs of permanent decay, there are numerous others which, while having already furnished conclusive proof of their productivity, have, for the most part, been but slightly developed. Each passing year registers the incoming of fresh oil-producing areas, while numerous regions in practically every part of the world, giving much promise of the success of ultimate oil developments, are as yet virgin territory. The cry of possible shortage of supply was, fortunately, made at the opportune moment: it was a word of warning, and was taken to heart especially by those associated with the development of the older producing oil-fields. In these fields--whether we look to America or Russia--there has always been considerable waste of crude oil, mostly in regard to furnishing power for oil-field operations, while the natural gases which exude from the wells themselves, and to which reference is made in another chapter, have, in times past, been allowed to pass uncontrolled into the atmosphere. To-day, however, we see conservation in every direction--thanks to the application of scientific and engineering knowledge, combined with the exercise of care--and there is no doubt that this new factor will tend in a greater degree than may at first be imagined toward the preservation of Nature’s stores of crude oil for unlimited time. With these few general remarks, let us proceed to briefly survey the principal oil-fields of the world, leaving those which are in the process of development or exploitation to later consideration.