Gas itself is not infrequently an important by-product of an oil lease. Almost invariably gas is associated with oil, although oil is not always found where gas is available. From many wells immense quantities of gas escape while drilling is in progress, and may occasionally wreck the machinery. Drillers have become expert in handling these difficulties and in casing off the gas and corking it up for future use. In many of the oil districts of the South and Middle West, natural gas from the producing areas has become the fuel of countless people who will never return to the use of coal, so long as this cheap and cleanly source of heat and light is available. Some wells yield as much as 25,000,000 feet of gas per day. With gas and water eliminated, the crude oil is pumped from the “field tank” to the “tank farm,” a collection of great containers built near the oil fields to take care of the output of wells which produce oil faster than the pipe lines carry it to the refineries. These containers are built of sheet steel and have a standard capacity of about 55,000 barrels in most cases, although some are constructed to contain 80,000 barrels. They are riveted and must be absolutely proof against leakage. Incidentally, it may be mentioned that one of the difficulties which human ingenuity cannot combat is the tendency of lightning to become attracted by these steel constructions on the open prairies. Great havoc and waste sometimes result. Another convulsion of nature also dreaded by the oil man of the Middle West is the cyclone, which at times is especially disastrous to derricks and pumping plants. There is but one more stage through which the crude petroleum passes on its way to the refinery, but this stage is so important and has been such a vital factor in the organization of the American oil industry, as well as in those of other countries which have emulated the system, that it demands extended reference. It is the pipe-line system which has done more to make the products of petroleum available to all at reasonable prices than any other innovation in connection with the industry. It is in reality like the waterworks system which reaches under the streets of modern towns and cities, but extending beneath the surface of millions of square miles of territory.