The intentional surges on 11 gas transmission pipes began in 2003 and included a spike in a pipe in San Bruno that exploded Sept. 9, killing eight people and destroyed 38 homes, the San Francisco Chronicle reported Sunday.
Brian Swanson, a spokesman for PG&E said the utility is still conducting a "very thorough examination of records" to establish the situation and setting of each pressure increase.
"We're continuing to verify how many times and when and which segments were involved," Swanson said. "We're still verifying records on all our other lines."
Experts at PG&E said spiking the pressure on the San Bruno line could have weakened it and the same danger exists for the other lines.
Democratic Assemblywoman Jackie Speier, who condemned the utility's practice as "Russian roulette," said federal prosecutors have begun a "civil and criminal review" of what led up to the San Bruno explosion, the Chronicle reported.