Continued pressure to reduce CO2 emissions and to improve fuel economy has resulted in many studies to increase engine efficiency. Increasing compression ratio is one of the most fundamental ways to reduce fuel consumption, but the compression ratio in practical gasoline engines is limited by knock. Presented in this paper is a study of the fuel economy opportunity of applying variable compression ratio technology to a modern downsized, boosted engine. Part throttle fuel consumption and full load performance were both considered. Load sweeps were conducted experimentally on a multi cylinder GTDI engine at several compression ratios and with a matrix of fuel octanes. Results from these experiments were compared to existing BTE vs CR correlations from the literature and were then used to estimate the metro highway fuel economy benefit of two step and continuously variable compression ratio concepts. The influence of compression ratio on exhaust gas temperature and peak cylinder pressure was also examined.