What else uses petrol?
The populace
Military production
Consumer goods
Power (if using petrol power plants)
Metal Ore production
If you do not have enough petrol to supply ALL of these, the AI will shut one down, or reduce production, for obvious reasons. If you have any reserved, it will use that first before applying the 'shortage'.
To resolve the 'shortage' try the following:
Set "sell excess production" to zero for petrol. (make sure your minister is locked out, or he will just max it out again)
Reduce consumer goods production to zero. (make sure your minister is locked out, or he will just max it out again)
Wait a full day, and see what it does to your petrol supply. Then, gradually increase consumer production again until it is as high as possible without causing a shortage. The difference, will show you how many petrol wells you will need to build to operate everything at max capacity.
You can also (at the same time) manually raise the price of petrol to the max, which can reduce consumer demand greatly, and more-so the longer you leave it maxed. The max price depends on the market price, so you might need to adjust it every day for a few days to get it high enough to reduce consumption.
