As of June 2014, it is unknown which particular species of tree produces the most oxygen. A variety of factors contribute to the amount of oxygen a tree can produce, such as the age, health and surrounding area of a tree.
It is known that mature, leafy trees, such as redwoods, aspens and oaks, are the best producers of oxygen. Additionally, it is known that a tree produces higher volumes when growing than when mature, because converting air and soil into wood causes the tree to produce more oxygen. A single, mature tree produces more than 6,000 pounds of oxygen per year.
https://www.reference.com/science/tree-gives-off-oxygen-7b76772d3c84d4fb
