Performance indices as measured by percentage of shortfall of energy generated, load factor, utilization factor and capacity factor of Sapele thermal power station, Nigeria in the period 1997 to 2006 is presented. The thermal station uses both steam and gas turbines. The station consists of six units of steam turbine and four units of gas turbine with total installed capacity of 1020 MW. But it was established that less than 17 % of the installed capacity was available. The percentage shortfall of energy generated for the period under review ranged from 27.4 to 49.1 %. This was due to aging of the plant, improper operation and maintenance. The load factor was between 39.9 and 64 % as against international best practice of 80 %. The inability of Power Holding Company of Nigeria (PHCN) to do turn-around maintenance on the plant was advanced for the dismal value. Average plant availability of the plant for the studied period was less than 21% as against Industry best practice of over 95 %. The capacity factor was even more dismal. For the period under review, it ranged from as low as 5.49 % in 2006 to the highest value of 17.19 % in 1997. Low capacity factor indicates excessive plant failure. Measures to improve the performance indices of the plant have been suggested such as training of operation and maintenance (O & M) personnel regularly, improvement in O & M practices, proper spare parts inventory, organizing regular management meetings and improving general housekeeping of the plant.