This is a rather perfect example of bad logic. The technical term for your particular mistake is
"post hoc". "It rained after I washed my car, therefore washing my car caused it to rain".
"Prices dropped after Bush allowed for greater US oil exploration/drilling, therefore when Bush allowed for greater US oil exploration/drilling it caused the price of oil to drop."
Further evidence of fail is that the price of oil futures which is the price of oil you see in the news, IS ONLY FOR DELIVERIES WITHIN THE NEXT 30 DAYS.
People who trade oil for a living know that it takes YEARS to fully develop a field and bring it online.