I recently encountered this while representing the oil fields at Nagykanizsa, Hungary. They were a treasured resource for Germany, even prompting the "Spring Awakening" offensive of 1945 in a failed attempt to prevent their capture by the Soviets.
So I wondered what became of these fields. Turns out they were more or less exhausted by the German war effort. I've attached an image showing their production from 1938 to 1949. The image comes from a 1950 CIA report--
https://www.cia.gov/readingroom/docs/CI ... 0589-2.pdf