Special ships look for oil fields under the sea. They use sound waves to build up a picture of the rock layers. This is called a seismic survey.
The only way to be sure if there is oil is to drill down into the rock.
This ship is making a chart of rock layers under the sea bed. This chart is called a seismic survey.
The chart is made using sound waves. The sound is produced by air guns towed behind the ship.
The sound is reflected of the bottom and picked up by special microphones - you can see them in the picture.