The amount of fluid a "walking beam" pumper can bring to the surface is affected by several factors, but one is the "stroke length," This is, in inches, the distance the oil-bearing rod in the well-hole moves up and down as the horse-head/walking beam pump makes one cycle.

Picture it this way: The oil is in the pay zone at the bottom of the oil well. The rod string is a connected set of many, many tubes connected vertically that stretch down the well-hole from the pump on the surface to down where the oil is found.

As the oil pump on the surface begins its "up-stroke," it pulls the rod string up out of the well-head this given length. This creates a vacuum at the bottom of the hole, sucking in oil until the pump comes back down. Then, a valve at the bottom of the rod string closes off, and one more "section" of oil is encased in the rod,

Okay, now I am going to ask you to conceive something rather bizarre, for illustrative purposes.

Picture the oil coming to the surface as a bunch of tubes. Each tube is an independent unit, like a test tube filled with oil, but with little arms and legs and a happy face.

Picture them all clinging to a tall ladder, that starts underground at the bottom of the well-hole and ends up on the surface.

Upon a given signal, picture the little tube-creature closest to the top climbing out of the well and jumping into a tanker truck. Now picture the next tube-creature below him quickly climbing up the ladder one tube-length to fill his vacated spot.

(Those of you who may find this mental image of arm-and-leg-and face little tubes coming out of oil wells too disturbing are invited to leave the room at this point and go watch TV or something; the rest of us will go on.....)

Now picture all the little tubes below that first guy doing the same -- each climbing up the ladder six rungs or so to fill the space opened above them by the movement of that first guy. At the well bottom, one additional tube of oil jumps onto the ladder as a new spot opens up. On the surface, the walking beam pump has reached the top of its stroke -- the counterweights then pull the beam and horsehead back down to the starting point. The walking beam moved upward a second time, and the "horse head" pulls the rod string up out of the well a second time, and ....

...And all our little tube-guys climb up the ladder one more section, as the top one jumps out of the well and a new one jumps on, down at the bottom.

Bizarre example? You bet! But that is how it works ... as the oil pump on the surface moves from down to up, all the little sections of oil along the rod string down into the hole to the very bottom of the well move up one such length! You may not sleep well tonight trying to get this cartoon image out of your head now ... but you will never forget how an oil well works!)

(Photo: Mary E. Hefley Well #4, corner of Morrison and Prospect streets, in 1984 -- Scott Bailey photo.)