Since 1870 the industry has spread all over the globe–Russia, Galicia, Rumania, Java, Borneo and Burma being prominent sources of the oil supply of the world. The raw petroleum of different localities differs in each case in the amount of solid paraffins and olefines dissolved in the liquid paraffins. Other substances also are dissolved in it in variable amount–such as benzene, acetylene, camphene and naphthalene. The fact that the oil, when reached by a boring, is often found to be under a considerable pressure, so that it rises and flows from the surface of the well, or even may shoot up as a great fountain, is an important feature in the oil-seeking industry, though the supply depends largely on pumping and not necessarily on natural flow. The borings when made, act like Artesian wells, and sometimes are carried to a great depth. Those in Pennsylvania vary in depth from 300 ft. to 3700 ft., according to the distance below the surface at which the oil-bearing strata (usually a sandstone) is situate. As in the case of an Artesian well, the boring is in the first instance an exploration subject to uncertainty as to "striking" the desired liquid, but the uncertainty is greater in the case of the search for oil than in that for water. The water-well is also far less likely to "give out" when once flowing than is that bored for oil, which, even if at first successful, may be soon exhausted owing to the small area of the oil-bearing strata tapped. A cause of the high pressure in many oil-wells is the gas which accompanies the oil. The pressure may amount to as much as 1000 lb. to the square inch. In the Northern Caucasus spouting wells caused by the high pressure of gas in the boring are frequent. A famous fountain-well in that region, which began to flow in August 1895, threw up 4½ million gallons a day, gradually diminishing during fifteen months until it became exhausted. At first, when boring was introduced, such outbursts led to an enormous loss of the oil, for there was not sufficient means of storing or transporting it. Ordinary cartage in barrels was the earlier method; then followed tanks on railway trains and canal boats; and this has been supplemented by the use of pipes along which the oil is pumped from the well to the refinery. In Pennsylvania there are said to be no less than 25,000 miles of such pipes in use for the distribution of petroleum.