Many years ago, fuel oil made its serious début, but at that time the supply of the product was very uncertain, and, consequently, progress in passing from the old to the new form of power-raising was slow. To-day, however, matters have materially changed. The crude oil output has been immeasurably increased, and many fields whose production of crude oil is essentially suited for fuel purposes have been opened up. In this respect, the oil-fields of Mexico have no parallel, and it is recorded that, once these fields are provided with adequate storage and transport facilities, they can easily supply the whole of the fuel oil necessary for the world, and at the same time have immense quantities to spare. But, though the subject of petroleum as fuel has aroused much attention for some years, there is still an erroneous idea prevailing as to what really is fuel oil. A word or two on this question will, therefore, not be without interest. Fuel oil is that portion of crude oil which is incapable of giving off by the process of ordinary distillation those lighter products of petroleum known as motor spirit, illuminating oils, or lubricants. It is, in a word, the residue of distillation which is unsuitable for refining purposes. It represents a black, tarry liquid, and is, of course, minus those fractions that go to produce the refined products. Many there are who refer to crude oil as fuel oil, but this is a misnomer, though crude oil, in many instances, is utilized for the purposes of fuel. In this chapter, however, when I speak of fuel oil, I am referring not to the crude oil as it comes from the ground (and which has a comparatively low flash) but to the article of commerce, the residue of distillation, which is the real article--fuel oil. The headway which fuel oil has made during the past few years has been remarkable, though it is safe to say that its general use is still in its infancy. In no matter what capacity it has been tried as a heating or steam-raising agent, it has proved itself capable of withstanding most successfully the most stringent tests, and has convinced all who have given the question serious consideration that it holds numerous advantages over coal, yet has no drawbacks. Perhaps the most recent impetus which has been given to the use of fuel oil is that following the introduction of it, and now its general adoption, throughout the units composing the British Navy. On land, however, it has for some years achieved marked distinction. Especially is this the case in regard to its use on locomotives, the United States railways alone consuming last year over 6,000,000 tons of fuel oil. In the realms of industry, fuel oil, too, is claiming the attention of those large industrial establishments, and to-day is largely used for creating intense heats, such as are necessary in hardening, annealing, melting and smelting, rivet heating, glass-melting, etc.