A pumping jack converts the rotary motion of its motor or engine into reciprocal up-and-down motion. Its reciprocating pump is connected to a series of pipes or tubes and sucker rods. The sucker rods have a one-way valve that allows oil to flow into the tubing on the downstroke but holds the oil in place on the upstroke. This continuous up-and-down movement lifts the oil to the surface. Wooden pumping jacks have been used since the early days of the petroleum industry, and smaller iron pumping jacks continue to be used regularly today.