In this study, the performance of different spark plugs was tested with varied spark gap sizes in a spark-ignited engine. Gasoline fuel was enriched with hydrogen and methanol to evaluate how much they affect the performance of the engine. The engine tests were performed with a four-stroke, single-cylinder, naturally aspirated, variable compression ratio (VCR) spark ignition engine. 1500 rpm engine speed and MBT for spark timing were applied throughout all experiments. Iridium, platinum and conventional (copper) spark plugs were tested using 3 different spark plug gaps (SPG) (0.6 mm, 0.8 mm, 1 mm). Depending on the experimental condition, hydrogen was added with 3 l/min of flow rate and methanol was used with 10% of volume fraction in the total liquid fuel. As for performance criteria, brake power (BP) and brake specific fuel consumption (BSFC) values were obtained from the test engine. According to the findings, platinum and iridium spark plugs had shown better performance than conventional spark plugs. The increment of SPG size improved the performance of the engine, too. On the other hand, despite methanol addition to gasoline fuel reduced performance, this loss could be compensated by hydrogen enrichment. Additionally, multiple linear regression (MLR) technique was applied through experimental results to obtain a linear relationship between explanatory variables (inputs) and response variables (outputs). An MLR model was set with four selected input variables (spark plug type, hydrogen flow rate, methanol ratio, and spark gap) to estimate BP and BSFC. Prediction equations showed that experimentally obtained results were in good agreement with MLR results. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.