In Spanish, the phoneme /s/ has two variants: [z] occurs in the coda when preceding a voiced consonant, and [s] occurs elsewhere. However, recent research has revealed irregular voicing patterns with regards to this phone. This dissertation examines two of these allophonic variations. It first investigates how speech rate and speech formality contribute to the gradient and variable nature of the voicing assimilation rule. Next, it explores possible intervocalic /s/ voicing in Highland Colombian Spanish. In accordance with other studies, the results showed partial voicing of coda position /s/ before voiced consonants (25%-80% voiced frication noise). Furthermore, there was scarce evidence for intervocalic /s/ voicing in the Colombian data (3%-35% voiced frication noise). Both studies led to the same conclusion; that gestural blending is a prominent and frequently occurring process in Spanish. In both cases, the vocal chords begin to vibrate in anticipation of the following sound (either a voiced consonant or vowel) before the constriction needed to produce the fricative has ended. The data revealed that there is a significant correlation between speech rate and the degree to which the adjacent segments overlap with one another. However, speech formality does not appear to be a function of the gestural overlap. In addition to the two factors tested (speech rate and speech formality), this dissertation also provides other possible factors which may affect the degree to which segments overlap such as its position within the syllable (onset versus coda) and following segment type (vowel versus consonant). [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]