The Massachusetts Association of Realtors (MAR) says the number of single-family homes put under agreement increased in May for the 13th straight month compared to the same period a year ago.

MAR said 5,267 single-family homes were put under agreement in May, up 32 percent compared to the 3,986 put under contract in the same month last year. This is the first time pending sales have gone over the 5,000 mark since MAR began tracking pending sales in January 2009, the association said

On a month-to-month basis, single-family homes put under agreement went up 10 percent from 4,784 homes in April.

The number of condos put under agreement in May (2,216) was up 35.5 percent compared to May 2011 (1,636). On a month-to-month basis, the number of condos put under agreement was up 18 percent from 1,878 units in April.

 A pending sale or a sale "under agreement" is when the buyer and seller agree on the terms of the sale of a home and have a signed purchase and sale agreement, but have yet to close and be recorded as such.