How is gas made?
Gas was made when decayed plants, bacteria and algae accumulated on the seabed or in swamps millions of years ago.
Gradually, layers of sediment fell on top, and the materials started to "cook" in the warmth and pressure. Oil began to form, and as the temperature and pressure increased, gas began to form too.
Once formed, the oil and gas started to move through the rock that contained them. This happened because the oil and gas expanded and took up more room than the original materials. The gas and oil were less dense than the rock around them so they tended to rise upwards. Where the gas and oil met an impermeable rock (a rock they could not pass through), the rock formed a seal and the gas and oil were trapped.
An animated diagram shows layers of rock, oil above this, gas above and rock or seal at the top. Pressure is shown pushing downwards and oil and gas are shown rising up through the rock.
