The financial impact of losing the olives was far less disappointing than the loss of information they could have provided, Australian Olive Expo organiser John Forrest said.

The trees, owned by the Expo and cultivated over four years, were for the first time yielding enough fruit to get useful trial data about which varieties grow better in certain conditions than others.

About 20 different varieties of trees were planted in 10 different configurations. The information would have been used to educate growers.

"It's really important that olive growers get good information and one of the issues is growing the right varieties for the conditions," Mr Forrest said.

"We put a lot of work into trialling varieties we think would grow in this environment."

But some time before the planned harvest on May 29, someone nabbed the olives, getting around the 2.5m tall fence topped with three strands of barbed wire. Not one olive was left behind.

Police officers came the next day, but no one had witnessed suspicious activity.

Mr Forrest said it was hard to specify a value for the lost olives because they weren't intended for commercial purposes.

They would have yielded about 20-30 litres of extra virgin olive oil.

Mr Forrest said anyone trying to make money out of the olives wouldn't get much.

He doesn't think it was an inside job and isn't too down-hearted - next year some data ought to be available if no-one strips the trees again. To guard against it, he may install a security camera.

The theft follows similar olive heists in NSW's lower Hunter, where up to 10 tonnes of olives were stolen from rural properties, apparently overnight, in recent months.

The thieves left no remnants on the ground and no sign of entry or exit.

Industry figures have speculated that birds or organised thieves took the olives.