Gasoline and petrol engines—terms often used interchangeably—represent spark-ignition internal combustion engines that rely on volatile, refined hydrocarbons to produce power. Although “gasoline” is the common term in North America and “petrol” is used across Europe, Asia, and many other regions, both refer to the same fuel type and the same general engine architecture. These engines operate on the Otto cycle, using spark plugs to ignite an air–fuel mixture, resulting in rapid combustion that drives pistons and generates mechanical power. Despite regional naming differences, gasoline/petrol engines are engineered with variations in compression ratios, fuel blends, octane ratings, and emissions control technologies based on local regulations and manufacturing standards. These engines offer several advantages, including smooth operation, wide availability, quick refueling, mature servicing networks, and strong acceleration performance. Their refined fuel and spark ignition mechanism allow for high-speed operation with minimal vibration. However, disadvantages remain substantial. Gasoline/petrol engines tend to be less fuel-efficient than diesel engines, particularly in high-load applications, and rely on fossil fuel combustion, which produces carbon dioxide, nitrogen oxides, volatile organic compounds, and particulate emissions. These pollutants contribute to climate change, smog formation, cardiovascular illnesses, and respiratory diseases. While modern engines equipped with catalytic converters, turbochargers, direct injection, and hybrid systems have significantly improved fuel efficiency and reduced emissions, environmental concerns continue to drive stricter regulations. Alternatives such as electric vehicles, hydrogen engines, and advanced biofuels challenge the long-term dominance of gasoline/petrol platforms. Nonetheless, due to their reliability, cost-effectiveness, and well-established infrastructure, gasoline and petrol engines remain widely used for personal transportation, small commercial vehicles, and light-duty applications. As global energy systems shift toward cleaner solutions, gasoline/petrol engines will likely persist in hybridized or highly optimized forms before gradually transitioning to low-carbon propulsion technologies across major vehicle markets.