Fuel is generally more economical than gas when considering long-term costs and energy efficiency. This conclusion is based on several factors, including the energy density of the fuels, their costs per unit, and the efficiency of the engines designed to use them.

Fuel, typically referring to gasoline or diesel, has a higher energy density compared to natural gas. This means that for the same volume, fuel can provide more energy, which can lead to better fuel efficiency and lower costs over time. According to the U.S. Energy Information Administration (EIA), the energy content of gasoline is approximately 125,000 British thermal units (Btu) per gallon, while natural gas has an energy content of about 1,020 Btu per cubic foot. This translates to about 1.3 gallons of gasoline being equivalent to the energy content of one cubic foot of natural gas.

However, the cost of fuel and gas can vary significantly depending on location, market conditions, and the time of year. Historically, fuel has been more expensive per unit of energy than natural gas. For instance, as of 2021, the average price of gasoline was around $2.50 per gallon, while the average price of natural gas was approximately $2.20 per thousand cubic feet. When comparing the cost per unit of energy, natural gas is often the more economical choice.

Moreover, the efficiency of engines designed to run on fuel versus gas also plays a role in determining overall economy. Modern internal combustion engines are optimized for fuel, and thus, they tend to operate more efficiently with fuel. This efficiency advantage can offset the higher initial cost of fuel compared to natural gas.

In conclusion, while the cost per unit of energy for natural gas is often lower than for fuel, the higher energy density and efficiency of fuel engines make fuel more economical in the long run. This is supported by data from the EIA, which shows that fuel has a higher energy content per unit volume and that modern engines are designed to maximize efficiency with fuel.