For the families that own Kennywood, it's a good time to sell, company President Peter McAneny said yesterday.

"It's getting to be a bigger and bigger group of owners," Mr. McAneny said.

Ann Dugan, who runs the Institute for Entrepreneurial Excellence at the University of Pittsburgh, said very few family-owned businesses last for more than a few generations.

She said only 40 percent of family-owned businesses make it to the second generation, 12 percent of those make it to a third generation, and 3 percent of the businesses that made it to three generations make it to four.

Kennywood Entertainment Inc. is in its fourth and fifth generations of ownership. The company announced Tuesday that it was being sold to Madrid-based Parques Reunidos, which owns amusement parks, water parks, animal parks and family entertainment centers throughout Europe and the United States.

"You have to look back and say what an amazing run these families have had," Mr. McAneny said.

Of the family-owned businesses that survive, Ms. Dugan said, even fewer are owned by two unrelated families.

She said the approximately 100 shareholders of Kennywood Entertainment have a natural tension between the family members who work for the company and those who don't. She said the shareholders who work for the company want to plow some of the profits back into the business while those who do not tend to be looking for higher dividends.

Some companies, she said, "prune" some of the branches of the family tree by buying shares from family members who are no longer involved in the business. Another tactic is to have a strong board of directors made up of family members and outsiders who want to do what's best for the company.

In the case of Kennywood, Mr. McAneny said "nothing can ever last forever. Maybe it's time to pass it on to somebody else."

He said in the past companies have approached the family to buy Kennywood Entertainment, which owns Kennywood Park in West Mifflin, Idlewild & SoakZone in Ligonier, Sandcastle Waterpark in West Homestead, Lake Compounce Theme Park in Bristol, Conn., and Story Land in Glen, N.H. Those overtures were rejected. In this case, however, the people at Kennywood received assurances that the parks would remain locally controlled so that visitors would not notice the difference despite the change in ownership.

"Give us a little credit," Mr. McAneny said about the people who work for the company. "We're all going to be here. It's really the people that are the critical element in any business but especially the entertainment business."