Kosmos Energy Ltd., a major player in exploiting a vast new oil field in Ghana, revealed it is the latest energy company grappling with the fallout from a U.S. crackdown on corporate bribery in foreign countries.

Kosmos said in documents filed last week with the U.S. Securities and Exchange Commission that it and its partners in the Jubilee field are looking into "potential violations" of the U.S. Foreign Corrupt Practices Act by one of the project's contractors. Their inquiry involves Modec Inc., a Japanese company that owns the specialized vessel Kosmos and its partners have hired to extract and collect crude oil from the offshore field, which is among the past decade's largest oil discoveries.

Modec didn't respond to a request for comment. In a July 2010 statement posted on its website, Modec said it was "undertaking a due diligence" of its service agreement with another contractor, at the request of one of Jubilee's owners. "Modec has retained outside independent counsel for this purpose," the statement said.

Production from the Jubilee field began last month, thrusting Ghana into the ranks of Africa's emerging oil producers and giving Dallas-based Kosmos, a private-equity-backed venture that owns a 23% stake in the field, the opportunity to reap a big return on its estimated investment of about $1 billion.

The International Finance Corp., a World Bank entity that helped finance the Modec vessel, is also investigating the situation, according to the filing, which Kosmos made in connection with a planned initial public stock offering. Lance Crist, the IFC's global head of oil and gas investments, said the agency is in the process of finalizing its due diligence on the matter.

The disclosure underscores the potential hazards that oil companies face when operating on frontiers such as West Africa. Many West African nations are ranked among the world's most corrupt by antibribery groups.

In recent years, the Justice Department has aggressively pursued violations of the FCPA, which bars U.S. companies from paying, or offering to pay, foreign-government officials or employees of state-owned companies to gain a business advantage. The department has warned that companies bear responsibility for the behavior of vendors and contractors. The number of FCPA enforcement actions increased by 85% from 2009 to 2010, according to law firm Morrison & Foerster.

The Justice Department declined to comment on the Modec matter or say whether it was investigating Modec or Kosmos. Companies often look into suspected FCPA violations on their own because department officials have said they may show leniency to companies that report their own violations.

In November, Royal Dutch Shell PLC and six other companies agreed to pay a combined $236 million to settle allegations they or their contractors bribed foreign officials to smooth the way for importing equipment and materials into several countries, including Nigeria and Angola. A Shell spokeswoman has said Shell cooperated with the probe and fired or disciplined employees in its aftermath.

Schlumberger Ltd., the largest oilfield-services company in the world, is being investigated by the Justice Department for possible bribery in Yemen. Other large services firms, such as Halliburton Co. and Baker Hughes Inc. have in recent years settled cases with federal authorities over bribery allegations in Africa and Central Asia.

Kosmos failed last year in its attempt to sell its stake in Jubilee—its major asset—to the world's biggest publicly traded oil company,Exxon Mobil Corp.

Now, Kosmos is counting on the field's income to attract investors to its planned IPO of $500 million worth of shares. Kosmos is majority-owned by the private-equity firms Blackstone Group LP and Warburg Pincus LLC.

Kosmos's filing said that the Jubilee partners' inquiry has triggered a suspension of Modec's loans with a syndicate of unidentified international banks. If Modec can't get funding, Jubilee's owners could be forced to buy its oil-producing and storing vessel before Sept. 15, 2011, in order to keep oil flowing. If they can't, and lose access to the ship, production would have to stop, according to the filing.

Analysts and Jubilee's owners played down the risk of that scenario, however. A spokesman for Anadarko Petroleum Corp., which also owns a 23% stake in the field, said "regardless of the outcome, we do not anticipate this will impact our costs or operations."