The effect of magnetic field has attracted many researchers to investigate the impact of this type of force on different applications such as combustion and water. Different systems supported by many patents were introduced to the market to treat these applications. In the present study, a series of experiments were conducted to explore the impact of magnetic fuel treatment on engine performance. The magnetic field was produced from two different sources based on permanent and electromagnetic coils. Two engines with different configurations were used. Three fuels were tested, gasoline and diesel as liquid fuels and natural gas as a gaseous fuel. Vast numbers of experiments at different operating conditions were conducted on the two engines. Fuel consumption, output power, and exhaust emissions were analyzed under the exposure of magnetic field. Gasoline was the most affected fuel while other fuels showed less or negligible effect. Magnetic field strength was a key parameter to have any impact on engine performance. Promising results were obtained evidenced by the reduction in engine fuel consumption and main pollutants.