Texas, USA. Cattle grazing in a grassy field with a 'nodding donkey' oil pump in operation in the background.

A 'nodding donkey' oil pump in operation viewed through leafless twigs in Texas, USA.

Close-up view of a 'nodding donkey' oil pump in operation silhouetted against a golden sunset in Texas, USA.

A 'nodding donkey' oil pump in operation silhouetted against a golden sunset in Texas, USA.

USA. A 'nodding donkey' oil pump in operation surrounded by leafy trees. Heat creates a visible haze effect in the air.

USA. Medium close up view of a rusted 'nodding donkey' oil pump in operation.

USA. Close-up view of a 'nodding donkey' oil pump in operation framed against a blue sky.

USA. Wide view of 'nodding donkey' oil pumps operating in a green oil field.

USA. A 'nodding donkey' oil pump in operation surrounded by palm trees.

Barrow Island, Australia. Low-angle view of a 'nodding donkey' oil pump operating against a blue sky background.

Barrow Island, Australia. A 'nodding donkey' oil pump operates on red soil against a blue sky background.

USA. Medium close up view of several 'nodding donkey' oil pumps in operation. Heat creates a visible haze effect in the air.

USA. 'Nodding donkey' oil pumps in operation framed against a blue sky.

Barrow Island, Australia. A 'nodding donkey' oil pump operates on a grassy plain against a blue sky.

Low-angle view of a 'nodding donkey' oil pump in operation framed against a blue sky.