This study was conducted by the University of Tokushima School of Medicine along with several other Japanese universities. It involved 11 Japanese women who consumed either water, green matcha tea, or oolong tea after a meal. The results were interesting. Oolong tea appeared to increase energy expenditure by 10%, green tea by 4%, and water not at all. This means that you burn more fat when you drink oolong or green tea after a meal.

The study also found that oolong tea has half the caffeine of green tea and half the levels of EGCG, green tea's cancer killing compound. The level of polymerized polyphenols was higher in oolong tea and is loosely associated with the weight loss results by the authors. All other polyphenol levels were identical between green and oolong tea. The differences between the two were seen as a result of the different processing performed on the teas.

References:

1. "Oolong tea increases energy metabolism in Japanese females", The Journal of Investigative Medicine, p170, Tatsushi Komatsu, Masayo Nakamori, Keiko Komatsu, Kazuaki Hosoda, Mariko Okamura, Kenji Toyama, Yoshiyuki Ishikura, Tohru Sakai, Daisuke Kunii and Shigeru Yamamoto