It's gas investment. Instead of paying x$ every time at the pump, you put a down payment on the gas for the current price. For example, the average price around my area is probably 4.10$. If I invested 1000$ in gas, I could save money by avoiding the current rising gas prices, so I would get gas for 4.10$ until my 1000$ ran out. ya dig?
Personally, I dont make enough money to make any such investments. I'm 17, and make shit money so I think I'm gonna stick to putting in 20$ every few days.