Because of nigeria’s instability, major oil companies like exxon-mobile have not invested in the country.

The statement is true.

Nigeria is anything but stable country and there are multiple factors that make too big of a risk for foreign big investments in the country, including the oil and gas industry. Some of the problems that push back investments are:

- Oil spills
- Pipeline vandalism 
- Crude oil theft
- Kidnapping
- Pollution
- Old deteriorated infrastructure 
- Terrorist organizations

It is true that Exxon-Mobile is devesting in Nigeria because of it's instability.

Explanation:

After 25 years, Exxon-Mobile corporation has been contemplating to exit its sale of the stake in Nigeria. It is planning to ramp off the divestitures by 2025. Due to the military violence and oil spills from the damages of the pipelines, many international companies including Exxon are seeking to lower their holdings. According to the Chairman of the Exxon Mobile Corporation, pollution in Niger delta, insufficient pipeline infrastructure, crude theft, fuel pricing, performance optimization are the areas to be re-looked for further investments.