This study aimed to explore 1) Thai learners' selections of single-word and multi-word units in English language production, and 2) the reasons for their selections of single-word and multi-word units. The participants in this study comprised 202 undergraduate students. Three research instruments were used in this study: a comprehension test, a word selection test, and an avoidance and preference questionnaire. The findings showed that in total, the learners tended to favor multi-word units more than single-word units. The results also indicated that the learners preferred literal phrasal verbs and compounds over their single-word equivalents. However, single-word units were preferred over figurative phrasal verbs and idioms by the learners. Based on the t-test results, overall, there were no statistically significant differences in the learners' selection of single-word and multi-word units. Nevertheless, the learners' responses to the avoidance and preference questionnaire reflected their preference for selecting both word types (single-word and multi-word units) more than their avoidance. This implies that preference may have a significant influence on their selection of word types, at least more so than avoidance. This may imply that preference have a higher effect on their selection of both word types than avoidance.