An image forming system includes a segregation tank to store a first imaging oil having a first percent purity, a reservoir to store a second imaging oil having a second percent purity, a slope identification module to identify a first slope value, and a slope comparison module to determine whether the first slope value is at least one of equal to, greater than, and less than a threshold slope value within a threshold slope range. The image forming system also includes a ratio adjustment module to obtain a variable ratio value corresponding to a ratio of a first amount of the first imaging oil to a second amount of the second imaging oil based on a determination by the slope comparison module.