(tar sands imported into the U.S. and that are refined in accordance with the same process that is used to refine crude oil and where no distinction exists between finished product that is refined from crude oil and tar sands are not subject to I.R.C. Sec. 4611 excise tax on petroleum; plain language of statute neither clearly includes or excludes tar sands from definition of "crude oil" and no regulations exist; Congressional history shows intent to exclude tar sands from definition).