The Derkul is a left tributary of the Donets located in the Luhansk Oblast of northeast Ukraine, on the border to the Rostov Oblast of Russia.

[2] The Derkul rises north of Markivka in the Ukrainian Luhansk Oblast on the western foothills of the Central Russian Upland.

In parts of the lower course, it forms a border of the Rostov Oblast of Russia.

The Derkul flows through the urban-type settlement of Bilovodsk at the lower reaches.

The most important tributary of the Derkul is the Polnaya from the left.