Mention oil spills, and images of birds coated in black slime and a shiny slick on the ocean’s surface come to mind.

But not all oil spills are the same.

About 672,000 gallons of oil spilled when a pipeline fractured about a mile below the ocean’s surface this month in the Gulf of Mexico southeast of Venice, La., which is about 65 miles south of New Orleans.

Hardly any of it was visible.

“The thing that sort of confused people about this one is that we weren’t seeing any oil,” Lt. Cmdr. Steven Youde of the Coast Guard said in a phone interview on Wednesday.

Aside from a few areas with a light sheen on the surface of the ocean, the oil seemed to have completely disappeared, and it was not expected to affect the shoreline.