The cost of olive oil is getting more expensive.

A new report says olive oil prices spiked 20 percent in 2015, after drought and disease devastated a big part of Europe's olive crop, and industry experts are forecasting a similar increase this year. Global production of the oil dropped by a third last year, according to data from the International Olive Council show.

Spain, which produces about 40 percent of the world's olive oil, experienced an unusually hot and dry summer in 2014. That led to the worst harvest in nearly 20 years, farmers say.

The 2015-2016 harvest is also turning out to be weak, again due to unusually hot summer weather. Three weeks of very high temperatures in July 2015 caused huge amounts of olives to mature too quickly. The International Olive Council now expects Spain to produce 1.2 million metric tons of olive oil this year, better than last year's disastrous harvest, but still way below the 1.8 million metric tons the country typically produces.

And it's not just Spain. Millions of olive trees in Italy, which produces 20 percent of the world's olive oil, have been attacked by a deadly disease.