The Pending Home Sales Index, measuring contracts that will likely close in June, rose 8.2 percent to 88.8, the trade group said.
Across the country, all of the regions tracked by the trade group saw gains.
In the Northeast, the pending home sales index rose 7.3 percent to 69.2. In the Midwest the index jumped 10.5 percent to 82.8. In the South, the index rose 4.1 percent to 95. In the West, the index climbed 12.9 percent to 100.6.
The regional data ranges from 4.4 percent above May 2010 in the Northeast to 17.2 percent higher than a year earlier in the Midwest.
"Absorption of inventory is the key to price improvement, and this solid gain in contract signings implies that home values in many localities are or will soon be stabilizing as inventories get absorbed at a faster pace," said NAR Chief Economist Lawrence Yun.
"Some markets have made a rapid turnaround, going from soft activity to contract signings rising by more than 30 percent from a year ago, including areas such as Hartford, Conn.; Indianapolis; Minneapolis; Houston and Seattle," Yun said.