Washington ? Oil executives disavowed internal memos obtained by congressional investigators that suggest a campaign to manipulate gasoline supplies to boost prices, especially in California and the Midwest.

The internal documents were cited Tuesday at a hearing by the Senate Governmental Affairs investigations subcommittee as evidence that oil companies plotted to reduce supplies to assure high prices in tight gasoline markets.

“Price spikes are becoming a way of life,” Sen. Carl Levin, D-Mich., the panel’s chairman, told the oil executives. He said there is strong evidence that companies worked to keep markets tight by curtailing supplies.

Levin repeatedly questioned a vice president of BP about a 1999 BP Amoco document that discussed numerous ways supplies could be cut to influence prices, including proposals to export gasoline to Canada or ship products other than gasoline to take up space on crowded pipelines. The document also said other companies might be influenced to cut production, or environmental rules could be used to curtail shipments.

Ross Pillari, a BP vice president for marketing, acknowledged the 1999 memo was discussed in a brainstorming session by senior executives, but said the proposals “were viewed as inappropriate” and summarily rejected.

Other executives said price spikes simply reflect market conditions and that refineries have worked aggressively to maintain supplies in a tight market. “There has not been any conspiracy,” said David Reeves, president of North American Products at ChevronTexaco.