Abstract: 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.