If you look at the ingredients list for any fat burning supplement, chances are that green tea will be on there.
This is because green tea has been shown to increase fat burning and boost the metabolic rate, in human controlled trials.
In one study in 10 healthy men, green tea increased energy expenditure by 4%.
Another study showed that fat oxidation was increased by 17%, indicating that green tea may selectively increase the burning of fat.
However, I'd like to point out that some studies on green tea don't show any increase in metabolism, so the effects may depend on the individual.
Caffeine itself has also been shown to improve physical performance by mobilizing fatty acids from the fat tissues and making them available for use as energy.
In two separate review studies, caffeine has been shown to increase physical performance by 11-12%, on average