NEW YORK - Buck Burns and David van Auker had not thought of the painting as a masterpiece until visitors to their New Mexico furniture and antiques shop began asking about it.

It turned out to be a painting by Willem de Kooning that was stolen 31 years ago from the University of Arizona Museum of Art.

Woman-Ochre- one of a number of abstract expressionist paintings that de Kooning did of women in the 1950s - was stolen in 1985.

On Aug 3, Mr van Auker phoned the museum and later the FBI.

The museum's interim director Meg Hagyard said it is very confident, based on its analysis, that this work is the original painting.

"We had the original frame and remnants, and we were able to match the painting with that. It fits like a glove with the canvas."

There was also evidence of previous conservation work that had been done.

The University of Arizona Police Department declined to say if it was still figuring out who might have stolen the work.

The reward for Mr van Auker's return of the painting?

"We're so excited to take him to dinner and to toast him," Ms Hagyard said.