The Fair Trade Commission inspected the offices of 20 companies, including Tokyo Gas Co., on Tuesday in connection with suspected bid-rigging on government-subsidized natural-gas filling station projects, sources said.

Other firms inspected on suspicion of violating the Antimonopoly Law include subsidiaries and affiliates of Osaka Gas Co. and Toho Gas Co., based in Nagoya, as well as Tokyo Gas's four subsidiaries. The head offices of Tokyo Gas, Osaka Gas and Toho Gas were also visited in connection with the case.

The firms allegedly rigged bids on contracts for the construction of natural gas stations on about 90 occasions starting in fiscal 2002.

The projects were for construction of filling stations for natural gas-powered vehicles. Commonly known as "eco-station" projects, they are ordered by gas suppliers, gas station owners and local governments.

The stations cost between 90 million yen and 120 million yen each. Between 3 billion yen and 4 billion yen has been spent annually since the program began. Most stations are subsidized by the Ministry of Economy, Trade and Industry.

Tokyo Gas and other gas companies reported to the Fair Trade Commission that internal probes had uncovered evidence of bid-rigging involving their eco-station projects.

Tokyo Gas said in June it had learned that four of its group firms, including Tokyo Gas Energy Co., were involved in bid-rigging and other unfair bidding practices on 63 occasions between April 2002 and last March. In 49 of the cases, one of the four Tokyo Gas firms won contracts for natural gas station projects, the company said.