The world's rainforests are responsible for producing between 20 and 30 percent of total the oxygen produced in the world each year. The Amazon rainforest alone produces nearly 20 percent of the world's oxygen.
However, the term "oxygen production" is quite misleading, as the decomposition of organic plant and animal matter in rainforests actually consumes about the same amount of oxygen as the forests produce. For this reason, the term "oxygen turnover" is preferred by many scientists.
The largest source of the world's oxygen is tiny microorganisms located in the oceans, which are estimated to contribute as much as 80 percent of the total oxygen produced each year.