There are many countries whose budgets are dependent mainly on revenues from oil production. Bigger countries with high dependence on crude oil export are Iraq, Saudi Arabia, Algeria, Lybia, Angola, Nigeria, Sudan, Kazakhstan, Venezuela, Iran.
Most economies from the middle east are quite dependent on oil production. Countries like Russia or Norway are also dependent on exporting of oil, but they have more diversified economies, so their budgets are not almost absolutely dependent on oil export.
Oil producing countries have different oil production costs. Some countries expect at least average oil market prices and other expect higher oil market prices. When the market prices are low, some oil producers are not able to make a profit, beacuse of their costs of oil production.