Because there is not enough quality crude oil in the states
There are around 3.5 million oil rigs, though some are not entirely used to drill for oil and most is on land. Many rigs are used to drill for water and geothermal heat. Usage of geothermal heating is common in Europe, and mobile oil rigs are used.
Because it's there. If there are oil reserves in a country you drill for them.
Drill for oil
to extract the oil out of the ground
An oil platform with an industrial drill.
It is the easiest way to find oil deposits.
The ability to drill oil has made the American economy and infrastructure what it is today. Everything that moves, seemingly is powered ultimately by oil.
An oil rig
Becuase oil refuses to drill itself.
One is called an oil drill.