The frequent flier perk system, which enables users to earn free plane tickets or in-flight upgrades, is the first among major U.S. airlines to preserve points indefinitely.
Before January 1, 2011, SkyMiles became invalid if no qualifying mileage activity, such as acquiring or redeeming miles, occurred for more than 24 months.
"This is an excellent move by Delta -- totally unexpected, though," he said. "Other carriers have implemented 36-month, 24-month, 18-month periods fliers can save their miles without activity. This is the first time an airline's gotten rid of an expiration date since mile perks became popular in the '80s."
Though everlasting miles may sound like a traveler's dream, Petersen said the development will affect a small portion of the flying population.
"Most people fly at least once every two or three years," he said. "If you do [fly] with Delta, you wouldn't let SkyMiles expire anyway. But this looks good for the program and helps them become a friendlier program."
Air travelers can expect other U.S. airlines to follow Delta's lead, Petersen said.
"It's good for consumers," he said. "It'll force other airlines to adopt a no-expiration policy so they don't look like oddballs."
Frequent fliers can typically redeem a free flight after seven or eight domestic round trips, Petersen said.