asphaltenes precipitated at the surface of the coupon is determined by comparing the weight of the coupon before the experiment to the weight at the end of the experiment the weight of asphaltenes collected on the coupon surface for a treated oil i e oil dosed with an asphaltene inhibitor dispersant is compared with that of an untreated oil from these two values the inhibitor dispersant efficiency is assessed using the following formula the amount of asphaltene deposited onto the coupon depends upon the efficacy of the asphaltene inhibitor an efficient and effective asphaltene inhibitor will result in less asphaltene mass deposited from the treated samples and result in a higher inhibition number from the equation above in turn an ineffective or non efficient or poor asphaltene inhibitor will result in an amount of asphaltene amount or weight deposited to the coupon that is closer to the weight of the control coupon i e the coupon that has been placed in the container with no asphaltene inhibitor during the experiment the precipitant can be added in any selected fashion e g drop wise all at once or in several fractions over the duration of the experiment a suitable amount of precipitant to be added to the crude oil during the experiment can be determined by titration of the oil with the precipitant prior to starting the experiment the amount of precipitant necessary to initiate asphaltene precipitation called onset volume is used as a guideline for the total amount of precipitant to be added to the oil during the deposition test generally a volume of precipitant corresponding to the onset volume u00b1 20 will be used during the deposition test the duration of the experiment.