The type of plant which produces the most oxygen is not known. This is a very hard question for scientists to determine since there are so many variables that have to be taken into consideration (plant living conditions, water level, supply of minerals and nutrients, geographical location, light conditions, climate, time of day and more). Also, consider that there are so many different types of plants and that they all need different living conditions to thrive. Changing even one variable will change the production of oxygen.

But there are some factors that may help determine oxygen production in general. A larger or faster-growing plant or one with a high photosynthetic rate will produce more oxygen than a smaller or slower growing one. Also, with two identical plants, the one receiving more light will likely produce more oxygen assuming the plants receive adequate levels of water, mineral nutrients and temperature.

Probably, the biggest oxygen producers will be the trees which have the fastest ability to convert the air and the soil they feed on into wood.

Another way of measuring the production of oxygen is to compare types of plants on a relative basis by comparing the oxygen produced per unit leaf area.