More than 110,000 Americans are on organ-transplant waiting lists, and demand for kidneys, lungs, hearts and other donated organs far exceeds the supply. Eighty percent of those waiting for organs need kidneys, in part because of rising incidences of obesity, hypertension and diabetes. States have made it easier for people to register as donors, either online or when obtaining or renewing a driver's license. Also, hospitals have been working to increase the number of families that allow a loved one's organs to be donated at death. But some transplant advocates are proposing more controversial measures, such as rewarding donors with financial compensation. Advances in bioengineering may eventually shrink the organ gap, allowing surgeons to transplant organs engineered from a patient's own stem cells. But for complex organs such as lungs and kidneys, that goal is probably decades away.