75% of the oil reserve in Sudan, perhaps 6.5 billion barrels, is located in South Sudan (Source).
Since the "second" Sudan war between the North and South started in 1983, an estimated 2 million civilians were killed, and at least 4 million were displaced at least once.
During the war, aid agencies set up one of the largest, most costly and complex humanitarian relief operations ever, "Operation Lifeline Sudan", running a "relief pipeline" from Kenya (and partially Uganda) into the South. An operation which was often criticised as "fueling the conflict".
True or not, I guess "Operation Bulletline Sudan" fueled the conflict much more: While Russia -mostly through proxies- and China -mostly thru "oil-for-bullets" deals- made good business of arms deals with the North, the "West" kept "an extensive arms pipeline" running to the South during the whole conflict.
For years, the world kept their eyes closed, as business was good: selling weapons dearly, and getting cheap oil, I mean, what more can one wish?
This US arms supply to the South continues to run up to this very day, mostly through Kenya, one of the strongest US proxies in the region. Meanwhile, Russia and China continue to supply Khartoum. What will this lead to? An expanded conflict border zone where North and South Sudan dispute oil fields.
Aren't we lucky there is an embargo for selling arms to Sudan?
PS: this map might indicate the oilfields more clearly (Tnx @MFB)