Delta has recently introduced one-way, one-class international upgrade awards, making it easier to upgrade from premium economy fares. There doesn’t, however, appear to be much rhyme or reason to the amount of miles charged. For example, when you upgrade one-way, one class to Japan from the United States it will cost you 12,500 miles from full-fare economy, but when flying to Israel expect to redeem 20,000 miles. Other redemption costs include:

• 10,000 miles for one-way, one-class upgrades from paid full-fare between the 50 United States, Bermuda, Canada, the Caribbean or Mexico and Europe, Expect to part with 20,000 miles when paying lesser fares.
• 10,000 miles for one-way, one-class upgrades from paid full-fare between the 50 United States, Bermuda, Canada, the Caribbean or Mexico and Argentina, Brazil or Chile. The redemption cost increases to 25,000 miles when paying a lesser fare.
• 20,000 miles for one-way, one-class upgrades from paid full-fare between the 50 United States, Bermuda, Canada, the Caribbean or Mexico and Israel, the Middle East, North Africa or India via the Atlantic. Lower fares require 25,000 miles to upgrade.
• 12,500 miles for one-way, one-class upgrades between the 50 United States, Bermuda, Canada, the Caribbean or Mexico and Japan via the Pacific. Select fares require 25,000 miles.