A 42 gallon barrel of oil can be refined into slightly less than 20 gallons of gasoline with the remaining oil distilled and refined into other products. The energy companies produce as much gas as they can since it's the most valuable product. So the asphalt and petroleum products used to make the plastic are essentially just what's left over from the production of gas.
The world is based on fossil fuel technology for the foreseeable future and we will be making fuel products to feed the demand, so the plastic bags are neither a waste of oil, or a primary reason for the exploration and refinement of the oil. So, I'll take plastic bags at the store.
