Buying the powerful painkiller fentanyl is as easy as doing a Google search, a new congressional report finds.

Congressional investigators posed as first-time buyers of the opioid and found six online sellers able to easily ship the drug from overseas to the U.S. The report released Wednesday found major deficiencies in tracking packages partly due to a lack of international cooperation.

The probe conducted by the investigations subcommittee of the Senate Homeland Security and Government Affairs Committee comes as localities are struggling with the proliferation of fentanyl, which can be 50 times more potent than heroin.

Fentanyl deaths have risen substantially in recent years. More than half of people in 10 states who died from an opioid abuse in the second half of 2016 tested positive for fentanyl, according to the Centers for Disease Control and Prevention.

“Thanks to our bipartisan investigation, we now know the depth to which drug traffickers exploit our mail system to ship fentanyl and other synthetic drugs into the United States,” said subcommittee Chairman Sen. Rob Portman, R-Ohio.

Sen. Tom Carper of Delaware, the top Democrat on the committee, added the report shows how “ill-equipped federal agencies were to prevent drug smugglers from taking advantage of a massive surge in recent years of e-commerce and international mail to ship synthetic opioids.”

Committee staffers started the investigation in May with a simple Google search looking for how to buy fentanyl. From there they identified six websites that responded quickly, some in less than 10 minutes, via e-mail to try and make a deal.

The online sellers wanted payment in the cryptocurrency Bitcoin, likely because it is difficult to track and cheaper than processing funds through a wire transfer or money order. Sellers, however, were willing to take credit cards or money orders.

The staffers did not actually buy any fentanyl, but asked various questions about payment methods and how the drugs would be shipped. Aides said they would be turning over the information on the investigation and the online sellers to law enforcement authorities.

The sellers primarily use the international arm of the U.S. Postal Service. Sellers emphasized that the Postal Service was the way to go because other avenues such as FedEx heighten the risk of seizures, according to the report.

The Drug Enforcement Administration has identified China as the main exporter of fentanyl. Sometimes sellers will route a fentanyl package through Europe to throw off suspicion. It is not clear where the six online sellers are based.

The committee subpoenaed payment records for the six websites through Western Union, the main money order service used by the fentanyl sellers, according to a Senate aide.

The records showed that the six sellers sent $230,000 worth of fentanyl to more than 300 U.S. residents.

Staffers found seven individuals who died of fentanyl-related overdoses after sending money to one of the sellers. They also identified 18 people arrested for drug-related charges that also made purchases and got packages from the sellers.

The report found major weaknesses in the system used to identify suspicious packages and interrupt their shipment. U.S. Customs and Border Patrol is responsible for identifying suspicious packages sent through international mail, but the Postal Service and express mail services such as DHL or FedEx are required to locate and physically hand over targeted packages for inspection.

But the Postal Service has to comb through more than four times the amount of packages than the express providers. In 2016, the three major express services handled about 65.7 million international packages, compared to more than 275 million for the Postal Service, the report said.

In November 2015, Customs and the Postal Service started a pilot program that implemented advanced electronic data, or AED. A shipper provides the data when a package is dropped off that includes the contents and a sender and recipient’s name and address.

Before a package reaches the U.S., the Postal Service sends the advance data to Customs, which analyzes it to see if the package is suspicious. The Postal Service then must locate and present the targeted packages to Customs officials.

But a major issue is there isn’t a requirement for all countries to provide AED on packages, the report added. The Postal Service only gets an AED on 36 percent of all international packages, the report notes.

Portman pointed to the need to pass the bipartisan STOP Act, which he co-sponsored and released last year. The bill requires shipments from foreign countries to include electronic advance data on what is in it and where it is going. Neither the Senate or House versions of the legislation have gone anywhere.

Carper also called on agencies to “redouble their efforts to keep illicit opioids from reaching our shores.”

Sen. Claire McCaskill of Missouri, the top Democrat on the full committee, called for the U.S. Postal Service’s watchdog to investigate how the agency identifies and seizes illegal opioids.