In addition to official trade with communist states, undeclared, uncontrolled, but government-tolerated trade with Thailand and with Singapore took place among private merchants, despite the trade embargo these two countries had imposed on Cambodia. Prime Minister Hun Sen reportedly declared that, "If the government can't carry out this trade and the people can, we allow them to do it."

Most of Cambodia's trade with Thailand took place in border and in coastal areas, particularly at the southwestern island of Kaoh Kong in the Gulf of Thailand. The illicit barter consisted of exchanging Cambodian dried fish, fresh crabs, shrimp, lobster, animal hides, elephant tusks, baby crocodiles, and gemstones for Thai clothing, sandals, toothpaste and toothbrushes, food, and bicycles. The total value of this growing illicit trade is not known, but some private sources estimated that it amounted to more than US$1 million a month.

Cambodia's illicit trade with Singapore was more visible. Ships registered in Singapore arrived regularly in Phnom Penh to deliver supplies to international relief organizations, operating in the country, as well as to private companies. International agencies estimated the value of undeclared trade with Singapore at US$2 million in 1985.

Data as of December 1987