In my research for “Operation Flash, Episode 4: Hungarian Rhapsody”, I stumbled (via WW II vlogger TIK) upon the book “Oil and the Great Powers: Britain and Germany, 1914 to 1945” by Anand Toprani (Oxford University Press, 2019: http://doi.org/10.1093/oso/9780198834601.001.0001 ).
One of the rationales that has been offered for Operation Barbarossa (the invasion of the USSR) was the extraction of resources, specifically grain from the Ukraine and oil from the Caucasus. The latter was not under Axis control for long enough, perhaps, but what about the (vampire) economic revenue from the vast territory that the Third Reich did occupy for considerable time?
Despite its preparation and ruthlessness, the Third Reich’s campaign to exploit the Soviet Union was as much an economic failure as a military one. The value of the resources Germany extracted from Belgium (9.3 billion RM) was double that from the Soviet Union (4.5 billion RM), while that from France (35 billion RM) was eight times greater.179 In terms of oil, Germany probably received more from the Soviet Union through trade before June 22, 1941 than it did through coercion during the occupation.Tofrani, p. 251
These figures do not include forced labor press-ganged in the above countries to go work in the old Reich
Lots to unpack in that book. For instance: I am somewhat familiar with the chemistry involved in the coal liquefaction (“synthetic gasoline”) plants through the Fischer-Tropsch and Bergius processes. What I did not realize was that this effort actually went back to the Weimar era: even when the production cost per barrel was considerably higher than the price of imported equivalents, the latter required foreign currency the Weimar republic was chronically short of. Coal was one of the few natural resources they were not lacking.
Apparently, between coal liquefaction, Romanian oil (from the fields in Ploesti, near Bucharest), some small wells in Austria and Hungary, and drastic rationing of civilian consumption, the Wehrmacht could sort-of make ends meet until the combination of Allied bombing campaigns and Romania defecting to the Allies in August 1944.
The German oil supply was tight throughout the war, and was a controlling factor in military operations. The chief source of supply, and the only source for aviation gasoline, was 13 synthetic plants together with a small production from three additional ones that started operations in 1944. The major sources of products refined from crude oil were the Ploesti oil fields in Rumania and the Hungarian fields which together accounted for about a quarter of the total supply of liquid fuels in 1943. In addition, there was a small but significant Austrian and domestic production. The refineries at Ploesti were attacked, beginning with a daring and costly low-level attack in August 1943. These had only limited effects; deliveries increased until April 1944 when the attacks were resumed. The 1944 attacks, together with mining of the Danube, materially reduced Rumanian deliveries. In August 1944, Russian occupation eliminated this source of supply and dependence on the synthetic plants became even greater than before.
Production from the synthetic plants declined steadily and by July 1944 every major plant had been hit. These plants were producing an average of 316,000 tons per month when the attacks began. Their production fell to 107,000 tons in June and 17,000 tons in September. Output of aviation gasoline from synthetic plants dropped from 175,000 tons in April to 30,000 tons in July and 5,000 tons in September. Production recovered somewhat in November and December, but for the rest of the war was but a fraction of pre-attack output. […] Consumption of oil exceeded production from May 1944 on. Accumulated stocks were rapidly used up, and in six months were practically exhausted. The loss of oil production was sharply felt by the armed forces. In August the final run-in-time for aircraft engines was cut from two hours to one-half hour. For lack of fuel, pilot training, previously cut down, was further curtailed. Through the summer, the movement of German Panzer Divisions in the field was hampered more and more seriously as a result of losses in combat and mounting transportation difficulties, together with the fall in fuel production. By December, according to Speer, the fuel shortage had reached catastrophic proportions. When the Germans launched their counter-offensive on December 16, 1944, their reserves of fuel were insufficient to support the operation. They counted on capturing Allied stocks. Failing in this, many panzer units were lost when they ran out of gasoline. In February and March of 1945 the Germans massed 1,200 tanks on the Baranov bridgehead at the Vistula to check the Russians. They were immobilized for lack of gasoline and overrun.