It is commonly held that Persian glottal consonants in syllable coda undergo vowel lengthening , . Some questions have been arised, however, concerning the phonological operations involved in CL. One view suggests that glottal allophonic weakening is compensated by vowel lengthening. Another view holds that CL involves the deletion of a coda glottal consonant followed by the lengthening of the adjacent nucleus vowel. There is a third view which suggests that CL is a gradient process in which different magnitude of glottal gesture is realized in speech from a weak through complete deletion of glottals. Using spectral tilt values, as defined by two measurements H1-H2 and H1-F1, I suggest that CL involves allophonic reduction of glottal gesture, which causes more length for the preceding vowel on the ground that glottals attain a gesture much similar to a vowel.