a method and kit for the on - site determination of the presence and concentration of contaminant materials in lubricating oils is provided . according to the method , chemical analysis of representative samples of the lubricating oil establishes the concentration of preselected metal contaminants that may be existing in the oil sample . concentration of acidic and / or basic contaminants is also determinable as a function of the ph value of the oil sample . repetitive analysis of oil samples , according to the method of the invention , provides information regarding the quality of the oil during its lifetime in machines and / or engines and provides a basis for determining when the oil should be replaced with oil containing little or no contaminant material . the invention also provides a kit for use in carrying out the method .