With the addition of ethanol to most gasoline sold in Hawai'i since April, gas companies were required to adjust their manufacturing process to make sure the new blend would meet standards aimed at preventing vehicles from stalling or having difficulty starting.

Tesoro Corp. informed the state that it would not meet the standards, and in March the state agreed to allow that.

Though the move increases the risk that people could have problems with their cars, the risk isn't large enough to warrant notifying consumers, said William Pierpont, manager for the Measurement Standards Branch of the state Department of Agriculture, which has oversight over the quality of fuel statewide.

"I'm not going to disclose there's a problem if there isn't a problem," Pierpont said. "If there is a problem, I'll disclose it."

Tesoro competitor and Hawai'i's only other refiner, Chevron Corp., did not seek any waiver of fuel standards and wants the state to warn consumers that Tesoro has been allowed to sell gasoline that doesn't meet the pre-ethanol standards.

Chevron has asked the Department of Agriculture to explain why Tesoro was granted a waiver from certain volatility standards and for an explanation of why the public was not notified.

"We're not challenging the decision (to waive standards) at this time," said Chevron spokesman Al Chee. "We're still in the mode of trying to understand what was the justification for this decision and is this the proper way to deal with it?"

Tesoro spokesman Nathan Hokama said the company sought relaxed standards because of manufacturing complications. He said the company plans to continue making gasoline under the state exemption.

"Because there haven't been any complaints and because they do have the waiver, they'll continue to operate as they have," Hokama said.

Although the ethanol-blended gasoline now sold by Tesoro does not meet prior industry standards, it is unlikely to cause problems for consumers, according to Tesoro and state officials. The change in volatility standards should affect only those autos operating in temperatures higher than 90 degrees Fahrenheit at an altitude of more than 5,000 feet, Pierpont said. Carbureted rather than fuel-injected autos would be more susceptible to drivability problems, he added.

Since the risks of problems from using Tesoro's gasoline are low, there was no need to disclose that the state lowered its fuel standards, Pierpont said.

"There is a higher risk of problems, but it should not be an issue," Pierpont said. "We do not believe this action will result in drivability problems."

The exemption was partly an attempt to prevent potential supply problems by giving refiners greater flexibility to sell fuel that does not meet the same volatility standards as non-ethanol fuel, Pierpont said. Tesoro manufactures about 588,000 gallons of gasoline a day, or about half of the state's supply.

The exemption was given to Tesoro after the San Antonio-based company asked state officials in January to relax the volatility standards for ethanol-blended gasoline. Tesoro said both Arizona and Kentucky have made similar accommodations allowing for the sale of ethanol-blended gasoline that doesn't meet volatility standards. Fuel volatility, or its evaporization quality, is affected by ethanol.

Unless gasoline is changed to compensate for the effects of ethanol, the blended fuel can cause vehicles to lose power, idle roughly, stall and have difficulty starting.

Pierpont said the state will monitor the quality of fuel and the public reactions and could revisit the decision to allow Tesoro to make out-of-specification gasoline.

Reach Sean Hao at shao@honoluluadvertiser.com.