The double overhand knot[1] or barrel knot[2][3] is simply an extension of the regular overhand knot, made with one additional pass.

The result is slightly larger and more difficult to untie.

"[4] When weighted, it can be difficult to untie, especially when wet.

Alternatively, the working end of the rope can be wrapped around the standing end twice, and then passed through both resulting loops.

[2][3] Both methods result in the same knot, though the latter is easier to dress in the compact finished form.