A court in China sentenced 15 people to prison for running a kidney trafficking operation in which donors were often paid less than $4,000 for their spare organ, according to Chinese news.

The global black market trade in human organs, estimated to be a $1 billion industry, fills a dire need for those with the money to pay. In the United States, 4,000 people die every year waiting for a kidney, according to a recent New York Times investigation into the underground kidney market. The World Health Organization estimates, generously, that available organs fill about one-tenth of the global need.

In China, more than 1.5 million people are waiting for organ transplants. The trafficking ring, sentenced last week in Beijing, included brokers who recruited donors and three doctors who performed the operations, the South China Morning Post reported. Donors, which the traffickers called “suppliers,” had their organs removed in a community health center several hours from Beijing. When the operation was complete, the ringleader drove the organs to a major hospital in the capital, in an ice box, for the second half of the procedure. They also performed operations inside a house they rented.

The group was convicted of harvesting 51 kidneys, and each was sentenced to prison terms ranging from 3.5 to 12 years. Clients paid upwards of $33,000 for the kidneys, but the suppliers, often discovered through social media, received only a fraction of that for their parts. The United Nations has said that more often, donors are tricked into giving their organs, and are frequently uncompensated. The Times investigation revealed that many Central American donors are recruited in taxis by a cabbie who vets them for financial desperation and refers them to a “friend” who could help.

In 2012, China broke up another trafficking ring after a 17-year-old young man agreed to sell a kidney for $3,500 so that he could buy an iPhone and an iPad. The perpetrators were convicted of intentional injury after the teen began to suffer from renal deficiency. China is considered one of the hotspots for organ trafficking, a practice which is illegal in every country but one: Iran, where there is virtually no waiting list for organs.