Nigeria is one of the countries with the largest reserves of crude oil worldwide. About 80 percent of the country's income comes from the export of oil and natural gas. In Port Harcourt, flares burn day and night. There are more than 120 gas flares in the Niger Delta. Here, natural gas that bubbles up during oil extraction is burned. It's a cheap way of getting rid of an undesired byproduct. Elsewhere, flaring has long been banned, because it releases greenhouse gases and carcinogenic heavy metals.