The development and validation of a simple spectrophotometric method for the measurement of container-closure integrity of an oil-based product is reported. An oil soluble dye, D + C Green #6 (DCG6), common name Quinizarin Green, with an absorbance maximum at 648 nm was employed. The sensitivity of the method was 0.1 microgram/mL corresponding to an absorbance of 0.002 AU which is three times the background absorbance level of 0.0006 AU. This concentration corresponds to dye ingress volumes of 0.1 microliter and 0.5 microliter for vial fill volumes of one milliliter and five milliliters, respectively. The repeatability, expressed as relative standard deviation (RSD) of six vials spiked at 0.2 microgram/mL of DCG6 ranged from 2.3% to 3.3%. Intermediate precision (RSD), as determined from 18 vials spiked at 0.2 microgram/mL of DCG6 was 7.8%. The linearity of absorbance with respect to DCG6 concentration was measured over the range 0.1513 to 6.053 micrograms/mL and demonstrated a linear relationship with a correlation coefficient of 0.9996. The method was shown to be specific for a sesame-based oil product, Haloperidol Decanoate Injection (HDI), at the wavelength of measurement.