The The operation manager of Mega Petroleum Station was finding it difficult in managing their queuing system and was not able to determine the best number of servers that can serve arriving customers at various demand periods which affects their queue performance. This study was conducted at Chester Mega Petroleum Station in Enugu, Nigeria with the aim of addressing the identified problem. The result from the Queue Evaluation Environment showed that 8 servers gave the best system utilization values of 73.2% which is expected to reduce the respective customers waiting times (Ws) by 84.7% for the case study establishments. The result further showed that with 8 servers for the service systems, there will be no more need of server increase at the respective average arrival rates of customers/minutes and also the expected probabilities of system idleness for the case studies were negligible at 8 server utilization. The Queue Evaluation Environment was later adopted in developing a Decision Support System for the referenced service facilities. The model was recommended for PMS refill only.