Petrol in Nigeria till today is been refined outside country and still import back to Nigeria on a high price, lots of minerals like coals, salt, kerosene, gas, petroleum and so on but no appropriate handling of this resources, so even the citizens can not benefit from it. If Africa can make use of their resources well, they will be more independent, free from indebtedness and indirect colonial system of other countries.
Supposedly with so many natural resources owned by African countries it can bring prosperity to all the people there, but unfortunately it didn't go well and there are still many people suffering in poverty when we read the news there. It's the same as my country which has abundant natural products, but people's lives in general are far from prosperous. To be honest, the government mismanaged and they have never been able to create prosperity for their people and that is why even though natural products are abundant people are still living on the poverty line.
Just imagine owning oil and exporting it overseas to be processed and re-imported to be sold at high prices in the oil-producing countries themselves. Whereas when the oil is processed in the country itself, it will generate jobs for local residents and can be sold at a more affordable price. The rest can be exported as refined oil to other countries, so that the country's income can be greater and prosperity can be created for a much larger percentage.