All adverbs ending in -ly and certain other adverbs, especially long ones, form the superlative by the addition of the word most or least. Some short or irregular adverbs, however, form the superlative by the addition of the ending -est.
The disinfection system works best with a 3% hydrogen peroxide solution.[well changed to superlative form best with ending -est]
The program is designed to work most efficiently in a 32-bit
environment. [superlative with most]
Most surprisingly, the experimental data matched our predictions
perfectly. [superlative with most]
If you are not sure how to form the comparative or superlative degree of a particular adverb, check the adverb in a dictionary.