Jacks that are installed nowadays often use an electric motor which starts and stops by a timer. There are small gasoline engines for this purpose too. Pumping jacks are not run continuously. Some are worked only two or three times a week. During the quiet periods, oil and salt water percolate from the formation into the hole, filling it to a level for pumping.
Operators watch the posted price of crude oil.
When it gets too low, they only pump oil in enough quantity to maintain the lease. We are not talking of great volume here. A settled stripper well in Pennsylvania may lift only a half barrel per week but some are better, especially if repressuring of the oil reservoir is carried out. The pump jack in the foreground is still hooked to the power by a rod line. This well is abandoned, but some oil may still be produced here.