16 
BULLETIN 102, UNITED STATES NATIONAL MUSEUM. 
itself; and by stretching out to meet a growing area of exploitation 
it has unified widely separated fields and enabled production to 
grow to its present imposing size. The pipe line has woven the 
scattered strands of adventurous exploration into a steady flow of 
bulk raw material. (See fig. 4.) 
Some crude petroleum is transported in tank cars, but most of the 
60,000 1 tank cars in operation in this country are engaged in moving 
petroleum products — gasoline, kerosene, and fuel oil chiefly. For 
transportation by sea, steel tankers and towing barges, fitted with 
noncommunicating compartments, are employed for both crude pe- 
troleum and its bulk products. The development of the tank steamer 
has been an important factor in building up an important foreign 
trade in petroleum products, is responsible for a considerable coast- 
wise movement of crude and fuel oil, 2 and has opened the oil fields 
of Mexico to the United States and other markets. 
REFINING. 
Crude petroleum may be burned as fuel and nearly a fifth of the 
domestic consumption is utilized in this way. 3 But most of the petro- 
leum is manufactured into a series of products which have wider 
1 Approximate number. 
2 The tanker is the only commercial rival to the pipe line ; movements of oil from the 
Gulf to North Atlantic ports, therefore, normally go coastwise instead of overland. 
3 A small proportion of the crude petroleum is used for dressing roads. 
