You mean dinosaurs are gas?
As the trees and plants died, they sank to the bottom of the swamps of oceans. They formed layers of a spongy material called peat. Over many hundreds of years, the peat was covered by sand and clay and other minerals, which turned into a type of rock called sedimentary.
More and more rock piled on top of more rock, and it weighed more and more. It began to press down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over millions of years, it turned into coal, oil or petroleum, and natural gas.
Fossil Fuels take MILLIONS of YEARS to form. This is why they are NON-RENEWABLE… We are using them up faster than they are formed. Once these fuels are gone, they are gone.