Concept:Kola nuts were one of the main agricultural exports of the Oyo Empire before colonial rule.Explanation:The Oyo Empire had a strong economy based on farming and trade.Among the goods traded, kola nuts were especially important because they were in high demand.They were valued for their use as a stimulant and in social ceremonies.Traders carried kola nuts from Oyo to other parts of West Africa and across the Sahara.While ivory and gold were also traded, kola nuts were a distinct and major export of the Oyo Empire itself.Answer:Kola nuts.