Oil was the main source of energy. Do you see Panzers suddenly beginning to use steam engines? And despite oil shipments from the Soviet Union, Germany before Operation Barbarossa was suffering from major shortages. If Stalin decides to cut off oil shipments to the Axis, either in order to soften relations with the Allies, or to invade Germany (invasion option is pretty unlikely), Germany will be in no state to do anything but hold the line for a while, before collapsing under the weight of the Soviet War Machine.
Source please? My (WoD) source says that they had just captured millions of tons of finished product (as opposed to feedstock) when they consolidated the gains made in Spring/Summer 1940. They also captured even more during the the foray through the Balkans in the Spring of 1941, again finished product. The crisis seen during Barbarossa (Aug. '41) had everything to do with a logistical system that couldn't keep up, and nothing to do with stocks at hand. The same can be said about the whole myth of not providing winter gear for the foot soldiers. It was made. It was packed and ready to send in October 41.
The fact is that when it comes down to throughput in the overstretched supply system, absolute priorities are: Ammunition, Food for the soldiers/Fodder for the draft horses, POL.
After that come another set: Spares (for field maintenance), Medical supply, Engineering supplies (to extend/improve the logistic network).
There was no shortage of motor POL/ammunition/sustenance at the rail heads in Aug. 41. There was no shortage at the point of embarkation either. The shortages were at the "pointy" end of an extremely overburdened ground (motor) transport system. There were serious shortages of
items that fall in the
second tier of supply
at one rail head in particular- HGM. Thus their supply system was incapable of anything more than what we saw historically...defensive actions, using what they had. Ammunition, sustenance, (and lastly) POL.
The North and the Ukraine axes were in a much better supply position and this was a fundamental factor in the decision to send Guderian south to Kiev when things went "sideways" at Smolensk. The situation (with regards to the relative burden on that particular Grosstransportraum/i.e. the motor transport system) south of the Prypiat marshes was much more suitable to allow full implementation of a Panzer Group on offensive operations (i.e. 500+ tons per day).
Read: The Most Valuable Asset of the Reich (Vol 2)-Meirzejewski (references the records of the DR)
Supplying War-Van Crevald (there's a full chapter on the Ostfront)
When Titans Clashed- Glantz/House (mostly tactical but there's logistic references galore)
The Wages of Destruction- J Adam Tooze (just because...)
FYI? Methinks that you are
somewhat out of your depth here...
Standing Stocks of finished POL
did become more of an issue by November/December, as the "booty cache" had been pretty well burned up...all three million tons of it. It should be noted that synth production was growing by leaps and bounds during this period. Investments in plant made in the late 30's were starting to pay off. Deliveries from Romania (erdol+ finished product) were also at their peak and the Zisterdorf field in Austria was coming on line.
As such, (contrary to "popular belief") Germany was not "starved" for POL in the 41-42 period. At the "pointy end" on the Ostfront and in N/A (Heer) there were always problems due to logistics. The Luftwaffe still had ample supply and suffered little/no operational effects in theatre- they just flew their supplies in when the ground system was overstressed.
On topic? The best time to strike was when they did. It was still a fool's errand to do so, but they had nothing to gain by waiting...
Ron