I am a contract driver.  

I drive to car dealers or companies needing a new truck to places in the country.  After the delivery, someone at the company signs the bill of lading.  I don't have a tow car, so then I take the train or bus back to my home station.  

The company pays an amount in the beginning of the trip for gas or diesel fuel.  I do the fueling at gas stations along my route.  I am paid an equal amount when I return with the signed bill of lading.  If the gas costs $300, then I get $300 when I return.  If the train or bus costs $150, I have profitted $150 (for example). The company reports to the government that I have made $600.  I have to file a Profit/Loss statement showing that my real profit was $150 (for example).