The lines have produced about a spill a month, ranging from less than a gallon to the 228,000 gallons of oil and produced water that spewed in 1999 onto land in the Kenai National Wildlife Refuge, the report said. At risk is the area's wildlife, commercial fisheries, recreation sites and public safety, the report said.

Titled "Lurking Below: Oil and gas Pipeline Problems in the Cook Inlet Watershed," the report analyzed data collected between 1995 and 2001 by the Alaska Department of Environmental Conservation (DEC).

Although most of the pipelines are old, dating back to the 1960s, that should not be an excuse for corrosion and leaks, said the report's author, Lois Epstein, an engineer and Cook Inlet Keeper staff member.

"I typically don't say that because something's old it's bad," Epstein said. If properly maintained, old pipelines can perform safely for many years, she said.

But that has not happened in parts of the Cook Inlet area, she said.

"If you don't do what it takes to prevent corrosion, then of course it's going to get worse over time," she said.

The Cook Inlet basin, which runs from Anchorage south to the Gulf of Alaska, is the state's oldest producing oil fields. Production began in the 1950s and the area now produces between 32,000 and 35,000 barrels a day. The area also produces natural gas and has about 700 miles of gas pipelines.

Unocal Corp, a major Cook inlet-area operator, came in for the most criticism in the report. The company's operates a little over a third of the area's pipelines, but its lines were responsible for about three-quarters of the documented spills and nearly all of the spilled volume in the period studied.

The area's eight biggest pipeline spills during the period occurred at Unocal's Swanson River oil field in the Kenai refuge. Those spills included the 229,000-gallon discharge, which was from a hole in a gathering line and was discovered by a snowmobiler.

Unocal defended its Cook Inlet environmental performance.

"Unocal's primary concerns are safety and the environment," the company said in a statement, adding it would review the Cook Inlet Keeper report "to determine whether there is any new information which may assist us in improving our program."

Other operators had good records, according to the report.

Those praised in the report as having "excellent" performance were Cook Inlet Pipe Line Co., a consortium that operates pipelines carrying oil from offshore platforms in the western part of the inlet, and Kenai Pipe Line. Neither had any reported spills, according to DEC records.

Cook Inlet Pipe Line is owned by Unocal, Marathon Oil and Phillips Petroleum Kenai Pipe Line is operated by Tesoro Petroleum Corp

Those operators' good records give reason for optimism, Epstein said.

"It is possible to do better. The question is how to get there," she said.