Colorado and several other Rocky Mountain states have minimum octane levels of 85 for regular gas, while most states with lower elevations have a minimum level of 87.
Research several years ago from the American Petroleum Institute showed that lower air pressure at higher altitudes allows vehicles to perform as well with 85 octane as they would with 87 at lower altitudes.
But a 2001 study by the Colorado Legislative Council, the state legislature's research arm, concluded that the altitude difference may apply only to older cars.
"Research findings indicate that newer vehicles manufactured in and after 1984 are equipped with sophisticated electronic control systems that minimize this altitude effect and may perform better using higher-octane gasolines," the report said.
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But it was only last week that ASTM International officials determined that the newer automotive technologies that apparently have rendered 85 octane less useful warranted a discussion about possible changes in Colorado.
Many car manufacturers recommend that motorists use at least 87 octane.
"They used to put in fine print that 85 octane was acceptable at higher altitudes, but mostly the manufacturers no longer agree with that," said Dick Piper, director of Colorado's Division of Oil and Public Safety.