China imports 66%-75% of its oil. That would drop dramatically in a hot war, as oil imports via the South China Sea would likely be blocked. This would require any imports to sail around Australia, which would likely be stopped by the US.
Russia would happily sell China oil, but it doesn't produce nearly enough to cover the gap.
No oil, no military. No oil, no economy.
I do not think oil is such a big problem. China import is 10mln barrels while Russia exports is 5mln barrels, Kazakhstan is 1.2mln barrels. I am sure they can transport Iranian oil if needed. What will also happen is that Russia will buy oil on international market to resell to China. There is no infrastructure now to transport that much oil but it can be built surprisingly fast. Germany just demonstrated that it's possible to built LNG terminal in six months. If you ignore property rights and all enviromental regulation and enlist military you can built trans-asia pipeline in a few months. China can also import oil thru Vietnam.
