Oil production in South Sudan has fallen by a quarter since independence four months ago, Unity State's environment minister has told the BBC.
Since the split from the north there has been a shortage of skilled workers, the minister, William Garjang, said.
The rainy season was also making it difficult to repair faulty machinery and several roads have been mined by rebels, he said.
Revenue from oil provides 98% of the new nation's budget.
South Sudan seceded from Sudan in July - the culmination of a peace deal signed in 2005 that ended decades of civil war.
The two countries have yet to agree on sharing their oil wealth.
The BBC's James Copnall in Bentiu, capital of Unity State, says there is growing concern about South Sudan's strong dependency on oil, particularly as the supply may run out in the next two or three decades. more