China and Russia invested $120 billion abroad in 2010, Transparency International (TI) said, noting it was "of particular concern" that the two nations ranked in the bottom two.
"Given the increasing global presence of businesses from these countries, bribery and corruption are likely to have a substantial impact on the societies in which they operate," the Berlin-based non-governmental body said.
Companies' ability to compete fairly in these markets could also be affected, it warned.
The watchdog, which next month releases its main report on global corruption, said its Bribe Payers Index ranked 28 of the world's leading economies on the likelihood of their firms to bribe public officials abroad, based on a survey of 3,000 business executives.
The countries were selected based on the value of their foreign direct investment outflows, the value of their exports and their regional significance, TI said.
Dutch and Swiss companies are considered least likely to bribe, followed by those from Belgium, Germany and Japan. Britain ranks joint eighth place with Singapore and the United States is in tenth.
The index also ranked bribery within business sectors, placing public works contracts and construction companies last, while agriculture and light manufacturing are seen as the least bribery-prone sectors.