What was the main purpose of crude oil in the United States before the advent of the automobile?

It was used for lightning in the form of kerosene.

Explanation:

The first oil well was dug by Edwin Drake in Pennsylvania in 1859 and he distilled the oil to produce kerosene which was used for lightning.

Edwin Drake also produced other petroleum products from the distillation but there was no use for them as at that time not until in 1892 when Automobile was invented and gasoline one of the distilled petroleum products was recognized as a valuable fuel