<P> The most important commercial sources for alkanes are natural gas and oil . Natural gas contains primarily methane and ethane, with some propane and butane: oil is a mixture of liquid alkanes and other hydrocarbons . These hydrocarbons were formed when marine animals and plants (zooplankton and phytoplankton) died and sank to the bottom of ancient seas and were covered with sediments in an anoxic environment and converted over many millions of years at high temperatures and high pressure to their current form . Natural gas resulted thereby for example from the following reaction: </P> <Dl> <Dd> C H O → 3 CH + 3 CO </Dd> </Dl> <Dd> C H O → 3 CH + 3 CO </Dd> <P> These hydrocarbon deposits, collected in porous rocks trapped beneath impermeable cap rocks, comprise commercial oil fields . They have formed over millions of years and once exhausted cannot be readily replaced . The depletion of these hydrocarbons reserves is the basis for what is known as the energy crisis . </P>

Name 5-carbon alkane with a tertiary carbon atom