But a spokesman for Japan Air Lines said it would not join but would stand by bilateral agreements it already had with members of the new alliance. The grouping will be second in size to the Star Alliance, which is headed by United Airlines and Lufthansa German Airlines and includes Air Canada, Scandinavian Airlines System, Thai Airways International PLC and Varig Brazilian Airlines. Alliances among airlines are an alternative to mergers in an industry that still is heavily regulated in much of the world and is widely ruled by agreements between governments. The oneworld deal does not entail any exchange of equity, the airlines said, and the participating airlines will keep their separate identities, as is the case with the Star Alliance. They also hope to catch and hold passengers by exchanging the benefits of their frequent-flier programs.
Critics counter that the alliances are a form of monopolization.
Already more than half of all airline passengers fly on a carrier belonging to one of the four current major alliances, and more than half of the world's jet fleet is operated by just 17 airlines. At the news conference in London, none of the executives from the five companies in oneworld would pledge that the deal would lead to lower fares. The European Commission is concerned that the growth of alliances is undermining the effect of airline deregulation in Europe. It is examining the Star Alliance, and Karel Van Miert, the commissioner in charge of competition, said oneworld would be viewed in the same context. This year, Mr. Van Miert also said he would investigate another airline linkup, the European Quality Alliance, on suspicions that it had established what he called a ''closed shop'' on some routes.