This article evaluates the impact of a submarine channel sand in the western Wilmington oil field, California, on hydrocarbon accumulation and leakage across boundary faults. The Wilmington field is in a broad anticline broken into 10 fault blocks by normal faults. The coarse-grained channel deposit, named T4, is identified in fault blocks I through III within the Tar zone, a lower Pliocene turbidite deposit and the shallowest productive zone in the area. The channel deposit incised into three sand units: T2, T5, and T7. Evidences of tilted oil-water contacts (OWC), OWC cutting structure depth contours, scattered oil traces, and fault seal analysis all indicate that the channel deposit is responsible for hydrocarbon leakage across the boundary faults. The leakage occurs in the three channel-incised sand units: T2, T5, and T7. In fault block I, hydrocarbons in the three sands charge the channel sand at the structural culmination, and then leak across the eastern boundary Wilmington fault into the wet S sand directly above the Tar zone on the hanging-wall block. In fault block IIA, hydrocarbons from the T5 and T7 sands pool in the channel sand on the north flank and leak across the eastern boundary Ford fault into the S sand on the hanging-wall block. This leakage across faults caused depletion of almost all hydrocarbon accumulations in the three channel-incised sands in fault block I. The leakage also raised OWCs on the north flank in fault block IIA, resulting in tilted OWCs in the two channel-incised sand intervals.