The oil was first discovered by vacationers earlier this week. A viewer sent ABC11 photos.
Investigators say it's unlikely the oil is coming from the huge spill in the Gulf of Mexico, but they're not sure what the source might be. There has been a concern the Gulf Loop Current might bring the remnants of the Gulf of Mexico oil spill around Florida and up North Carolina's coast.
According to Brunswick County Emergency Management Director Anthony Marzano, the tar balls being seen may have either come from oil seeping up from the ocean floor or could be from a ship that emptied its waste.
"We have no reason to believe these have come from the Gulf oil spill but we are prepared for that if it eventually comes this way," Coast Guard Commander John Nadeau told ABC11.
Nadeau says his crew collected about 30 tar balls over a 3-4 mile stretch of Oak Island and Caswell Beach.
"They ranged in size from a penny to a pancake," he said.
Naduea says it's something the Coast Guard deals with almost daily and that the public is likely more aware now because of the Gulf spill. He says oil is in water all the time either naturally or from ships and boats. The heavier components that don't evaporate get weathered by wind and waves, and then sink and collect sand. In warmer water, they become more buoyant and wash up on shore.
"If you ever step on a sandy clump on shore and the inside is gooey with tar, that's a weathered tar ball," he explained.
Officials say it's common for these to pop up every once in a while from the ocean floor or from passing ships.
Others say they've never seen anything like it.
"This is our eighth season and I've never witnessed anything like it," pier owner Dave Cooper said. "Oily products to me cause great concern because we have a business that relies on natural resources, anything that would be detrimental to that would be great financial concern to us."
The coast guard says contractors will clean up any remaining tar on Friday. It'll be tested to determine the source.
Experts say any oil from the gulf would likely take at least another month to arrive in North Carolina.
Anyone who sees the tar should call the Coast Guard (800) 424-8802. They always want to investigate the source. There is an Oil Spill Liability Trust Fund paid for with taxes on oil companies. This fund covers the cost of "mystery spill" clean up until a source can be determined and that company or ship owner can repay cost.