In 1938, of the total consumption of 44 million barrels, imports from overseas accounted for 28 million barrels or roughly 60 percent of the total supply. An additional 3.8 million barrels were imported overland from European sources (2.8 million barrels came from Romania alone), and another 3.8 million barrels were derived from domestic oil production. The remainder of the total, 9 million barrels, were produced synthetically. Although the total overseas imports were even higher in 1939 before the onset of the blockade in September (33 million barrels), this high proportion of overseas imports only indicated how precarious the fuel situation would become should Germany be cut off from them.
At the outbreak of the war, Germany’s stockpiles of fuel consisted of a total of 15 million barrels. The campaigns in Norway, Holland, Belgium, and France added another 5 million barrels in booty, and imports from the Soviet Union accounted for 4 million barrels in 1940 and 1.6 million barrels in the first half of 1941. Yet a High Command study in May of 1941 noted that with monthly military requirements for 7.25 million barrels and imports and home production of only 5.35 million barrels, German stocks would be exhausted by August 1941. The 26 percent shortfall could only be made up with petroleum from Russia. The need to provide the lacking 1.9 million barrels per month and the urgency to gain possession of the Russian oil fields in the Caucasus mountains, together with Ukrainian grain and Donets coal, were thus prime elements in the German decision to invade the Soviet Union in June 1941.