Saudi Arabia led a big drop in seaborne oil flows in June, with the world’s largest crude exporter likely keeping some barrels domestically to feed its power plants during hot weather.

Global seaborne flows fell by about 1.08 million barrels a day, according to ship-tracking data compiled by Bloomberg. The month-on-month drop was the biggest this year and about half of the decline came from the kingdom.

Saudi Arabia typically burns more crude in its power plants during summer months when demand for air conditioning rises. That leads to a drop off in flows to export markets, although the precise timing and scale of such declines varies each year.

Alongside Saudi Arabia there were also notable decreases from Iran, Iraq, West Africa, the US Gulf and the North Sea. Shipments from Brazil, Qatar and of Russia’s flagship Urals grade rose.