Gas-To-Liquid (GTL) is a refinery process to convert natural gas into longer-chain hydrocarbons such as gasoline or diesel fuel. Gas-To-Liquid or GTL is the most recent version of the Fischer-Tropsch process first advanced about 1923. Why the interest now? Simply put it is because of the vast amount of methane gas, CH4 that is available.
A simple look-----CH4, methane is the shortest of the paraffin series hydrocarbon chains that satisfy the formula --------CnH(2n+2). You can satisfy this by substituting n=1 and voila CH4. Now for car gasoline the values of n range from 4< n <9. For diesel the range is 9< n <15. BTW fuels manufactured in this manner are free of extraneous materials i.e. more pure.