It's common knowledge to know that organ donors save lives, but just how many do they save?

A new study reveals that in 25 years of organ donation the world saved more than two million lives. 

The United Network for Organ Sharing began keeping track of all organ transplants in the U.S. in 1987. The study began in September of that year through December 2012.

The researchers then reviewed the records of 1,112,835 patients - of these patients 533,329 underwent a transplant and 579,506 were placed on the waiting list but did not undergo a transplant. 

"The critical shortage of donors continues to hamper this field," the researchers wrote in the study. Based on the two million lives saved via organ donation since 1987, the researchers suggest that if more people become donors there will be "tremendous potential to do even more good for humankind in the future." 

Broken down, the results show that kidney transplants saved 1,372,969 life-years; liver transplant, 465,296 life-years; heart transplant, 269,715 life-years; lung transplant, 64,575 life-years; pancreas-kidney transplant, 79,198 life-years; pancreas transplant, 14,903 life-years; and intestine transplant, 4,402 life-years. 

Although many lives are being saved by organ donations, there is also a number of people who die on an organ waiting list because there are more critically ill patients than there are donors. 

An average of 79 people receive organ transplants every day, but there are still 21 people each day who die waiting for transplants because of the shortage of donated organs, according to the U.S. Department of Health and Human Services. 

The study was published in JAMA.