A comparative study on combustion characteristics and performance of a dual-fuel engine fueled with natural gas/methanol and natural gas/gasoline was conducted experimentally. All experiments were performed at an engine speed of 1600 r·min−1 with a brake mean effective pressure of 0.387 MPa. Energy substitution ratio (ESR) was defined as the energy released by methanol or gasoline to the total energy released. Four ESRs namely 0, 19, 33, and 44 % were conducted in this study. The results demonstrated that both methanol and gasoline addition accelerated the burning rate of natural gas, leading to an increased peak cylinder pressure (Pmax) and maximum heat release rate (HRRmax). The corresponding crank angle of Pmax and HRRmax advanced and approached to top dean center after methanol or gasoline enrichment for the specific spark timing (θig) and ESR. In addition, as the ESR grew from 0 % to 44 % with a θig of 25 °CA BTDC, the brake thermal efficiency (BTE) increased from 27.3 % to 28.1 % for the natural gas/methanol mixture. In contrast, BTE reduced from 27.3 % to 25.5 % for the natural gas/gasoline mixture. The total hydrocarbon and carbon monoxide emissions of natural gas engines can be lowered by adding methanol and raised by inputting gasoline. •A comparative analysis was conducted on natural gas engine with methanol and gasoline addition.•Brake thermal efficiency increased by adding methanol, but decreased by inputting gasoline.•BSTHC and BSCO emissions were lowered by adding methanol, but raised by inputting gasoline.