This is why Alberta has most of Canada's oil and gas. Geologists look at aerial photographs of the land's surface to look for areas that might have oil. Geologists chip pieces of rock from the ground and study them. Geophysicists use very sensitive instruments called magnetometers and gravitometers to make maps of the rocks below the ground. They study the magnetism and gravity.
Geophysicists also use seismographs.
They set off and explosion, and measure the echoes of the sound waves from the explosion as they travel through the rocks. Another method they use is core drilling. When oilmen drill for core samples, they pull up cores from the rocks. A core is a long cylinder of rock. After everything has been tried, the only way to find out for sure is to drill a wildcat well.