For Mexican drug cartels, marijuana remains big business, but they're turning their attention to an even more potent product now crossing the border into the United States.

It looks like motor oil, but the black watery tar sitting in five-gallon buckets is nearly pure THC concentrate.

"I started to see the people that would usually backpack marijuana through the desert were now backpacking up crude oil," said Detective Matthew Shay with the Maricopa County Sheriff's Office.

Cartels make the concentrate by using a complex process to strip THC off marijuana plants. What's left is distilled and filtered further, taking a product that began at about 6% THC into one that carries a THC content of more than 80%.

Shay says it takes about 250 pounds of low-grade commercial marijuana to produce a five-gallon bucket of crude cannabis oil. Once in a concentrated form, profits skyrocket. Each bucket could produce more than $500,000 in vaping cartridges.

"These are all black-market cartridges — none of these are from a licensed dispensary," Shar said.

Once the crude oil from the cartels hits the streets, dealers in the United States begin cutting the product with additives. Shay confirmed that dealers will add ingredients like vitamin E acetate — a compound linked to EVALI, a lung illness related to vaping that has sickened thousands across the country. However, a link between black market cannabis concentrate and EVALI has not yet been confirmed.

Shay confirmed that American smoking habits are driving the new trend. Using vape cartridges to deliver THC is now the most popular way of consuming marijuana.

"That's the whole business right?" Shay said, "If there isn't a market, there's no reason to be shipping the stuff up."

It's that demand that fuels the cartel's new strategy — creating a risk no one should take.

"The black market cannabis cartridges are going to be hazardous, period," Shay said.

Labs are testing the crude oil to find out exactly what kind of chemicals are in the product.

This story was originally published by Cameron Polom on KNXV in Phoenix.