Microbially influenced corrosion (MIC) is a common problem in biodiesel storage tanks. Here, thick microbial growths develop at and span aqueous/non-aqueous fluid interfaces. MIC in this setting was investigated in experiments using zero-resistance ammetry (ZRA) measurements. To mimic the water-fuel interface, one carbon steel coupon was deployed in B20 biodiesel and one carbon steel coupon was deployed in medium mimicking storage tank sump water, and current between the two coupons was measured. ZRA incubations were inoculated with fungi isolated from contaminated B20 biodiesel storage tanks. Corrosion on both coupons was the greatest in incubations with a fungus whose filaments penetrated the diesel fuel layer, while organisms that did not explore the fuel induced corrosion only on the coupon immersed in water and not on the coupon immersed in the fuel. Subsequent ZRA experiments indicated that current between steel coupons was only achieved when fungal hyphae penetrated the non-aqueous layer, and this resulted in the most extensive corrosion of the coupons. We call this corrosion aqueous/non-aqueous interfacial MIC (ANI-MIC).