350 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [hum,. 213. 
This maximum pressure has never been even approximately measured. 
Some elosed pressures of 500 pounds and over per square inch have 
been reported, but these are not well vouched for, and the only reli- 
able measurements vary from 79 to 350 pounds. 
While the cause of this pressure is not certainly known, it appears 
highly probable that it is due largely, if not entirely, to the expansive 
force of the associated gas. When the oil rock is penetrated by the 
drill it is usually necessary to remove the water from the casing by 
bailing. When the pressure is thus relieved there is first a rush of 
gas, followed by a stream of oil, which is expelled with great violence. 
The oil, however, never flows in a steady stream, like water from an 
artesian well, but by a series of jets or pulsations. These may be 
relatively slow, each flow lasting for several minutes, followed by an 
equal or longer period of quiescence in which only gas escapes; or 
they may be rapid, several pulsations occurring in a single minute. 
The rapidity of the pulsations appears to depend, among other things, 
upon the depth to which the well is drilled into the oil rock. Their 
rapidity and consequently the yield of the well is generally increased 
by deeper boring. 
In addition to the expansive force of the gas there is also probably 
some hydrostatic pressure in this field, but its influence in producing 
the phenomena of a gusher must be relatively insignificant. The 
existence of a slight hydrostatic pressure in the Spindletop pool is 
shown in the invasion of some wells by salt water, which was first 
noticed after the pool had been producing about eighteen months. 
This invasion will continue as the oil is removed, though the head may 
not be sufficient to bring the salt water to the surface. 
If the pressure producing the gushing in an oil pool is due chiefly 
to the expansive force of gas, it follows that this force will expel only 
a part of the oil, and the remainder will necessarily be won by pump- 
ing or by supplying the place of the natural gas by compressed air. 
It is evident, therefore, that the gas should never be allowed to escape 
freely from an oil pool, for, aside from the waste of a valuable fuel, 
the force needed to expel the oil is at the same time being lost. 
The history of the Spindletop pool is very instruct ive in this con- 
nection. The Lucas gusher came in in January, 1901, and was wild 
for nine days, during which the flow is variously estimated from half 
a million to a million barrels. Drilling at once became very active, 
and within a year about 200 wells had been completed within the 
productive territory, which was then well defined. The pressure 
undoubtedly began to decline within three months or less after the 
field was opened, though it was still so high that the decline was not 
readily noticeable. At the end of the first year of production the 
pressure, although still manifesting itself occasional^ with almost 
explosive violence, was perceptibly lowered. New wells rarely gushed 
spontaneously, as at first, but required bailing to remove the entire 
