Environmental contamination by petroleum hydrocarbons from anthropogenic sources can be a cause of stress for free-ranging wildlife. The response of wildlife to chemical contaminants requires that the hypothalamic–pituitary–adrenal (HPA) axis be precisely regulated to allow for proper glucocorticoid-mediated adaptive responses. Chronic oral exposure to low concentrations of bunker C fuel oil causes the development of adrenal hypertrophy in male ranch mink (Mustela vison) without increasing serum or fecal glucocorticoid concentrations. This hypertrophy is an adaptive response to fuel oil-induced adrenal insufficiency. To determine if the same phenomenon occurs in female mink or male mink exposed to artificially weathered fuel oil, female mink were fed 0 ppm (mineral oil) or 420 ppm fuel oil and male mink were exposed to 0 ppm, 420 ppm fuel oil, or 480 ppm artificially weathered fuel oil in the diet for 60–62 days. At the end of the exposure, serum glucocorticoid concentrations were assayed along with body and organ weight measurements. Fecal glucocorticoid concentrations were assayed at time points throughout the exposure. Male mink fed fuel oil or weathered fuel oil and female mink fed fuel oil had adrenal enlargement without any significant increases in the serum or fecal concentration of glucocorticoids, which is consistent with fuel oil–induced adrenal insufficiency. To address the physiological consequences of adrenal insufficiency, fuel oil–exposed male mink were administered an adrenocorticotropic hormone (ACTH) stimulation test. Fuel oil–exposed animals had a smaller incremental increase in serum glucocorticoid concentration after ACTH challenge compared to control animals. Our findings provide further evidence that the HPA axis of fuel oil–exposed animals is compromised and, therefore, not able to respond appropriately to the diverse stressors found in the environment.