Index of Effluency (or IOE) is the top prize awarded in the 24 Hours of LeMons automotive racing series. General criteria to win this award is a car that is too unreliable to be driven effectively on the streets yet manages to complete a decent number of laps on the race track. IOE can be awarded to a vehicle that was deemed unreliable from the factory (e.g. Volkswagen Karmann Ghia) or a more reliable car with an unwise engine transplant (e.g. Ford Thunderbird with a BMW diesel engine). The award is named after the "Index of Thermal Efficiency", a prize briefly given in LeMons' namesake the 24 Hours of Le Mans to the car that scored the highest based on a complex formula that took into account car weight, fuel usage and average speed.