A pipeline company said that maintenance issues prevented the immediate detection of a leak that spilled oil into a California ravine last week.
A spokeswoman for Crimson Pipeline told the Associated Press that the pipeline was emptied earlier in the week in order to replace valves.
The pipeline remained below full capacity at the time of the spill, which kept operators from noticing a drop in pressure.
Authorities were instead alerted to the spill by a nearby resident who noticed a noxious odor in the area.
More than 25,000 gallons were spilled before the pipeline was shut down, but Ventura firefighters constructed a dirt barrier that prevented the crude from reaching the ocean.
The cause of the spill itself remains under investigation.