The combined government estimate for the 2010 H3 with a 3.7-liter five-cylinder engine and automatic transmission is 16 miles per gallon. This represents a highway rating of 18 miles per gallon and a city rating of 14 miles per gallon.
While ratings for a similarly equipped H3 with a five-speed manual transmission remains the same for highway and city driving conditions, the overall rating drops to 15 miles per gallon. Increasing the engine size to the 5.3-liter V-8 engine drops the combined mileage to 14 miles per gallon with regular unleaded gasoline. However, drivers using E85 see a significant drop in fuel economy, with a combined rating of 10 miles per gallon.