At the time the first oil well was drilled successfully in Titusville, PA, in 1859, oil was transported in barrels. Within a very short time, as more wells were drilled in that region of northwestern Pennsylvania, the cost of transporting oil far outstripped the cost of removing it from the ground. With the invention of special railroad cars to transport oil, the cost of transport was reduced. Oil trucks, such as the one depicted on this stamp, further reduced the cost of oil transport and aided in the widespread use of petroleum products so soon after the first "discovery" in large quantity. This stamp was issued to meet the rate for bulk third class mail presorted to the five-digit ZIP code.