Read this: In the early 1980s, rapidly rising oil revenues enabled the government to finance large-scale development projects with GDP growth averaging 5% annually, one of the highest rates in Africa. The government has mortgaged a substantial portion of its petroleum earnings, contributing to a shortage of revenues. January 12, 1994 devaluation of Franc Zone currencies by 50% resulted in inflation of 46% in 1994, but inflation has subsided since.

What contributed to an excess of revenues?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable