I doubt it would have made much difference. Germany doomed it's oil supplies as soon as it declared war: over 60% of their oil was obtained from overseas suppliers. The lion's share of their domestic supplies was produced synthetically from coal. The synthetic fuel plants operated throughout the war, but only became invaluable to the German war effort in '43 (owing to the depletion of oil reserves by the Russian Campaign and the failure of the Germans to secure the oil fields in the Caucasus).
There is an interesting history of German wartime oil production here:
http://www.airpower.maxwell.af.mil/airchronicles/aureview/1981/jul-aug/becker.htm