This study compared Korean adult learners' English speech in dialogic and monologic tasks, measuring 57 college students' oral proficiency in terms of holistic and analytic grades. The statistical analyses were focused on two questions: (1) how much do the holistic grades of oral proficiency and analytic grades of the four linguistic features function differently across the tasks? and (2) which linguistic feature has the strongest correlation with the holistic grades of English oral proficiency? The study found significant differences between the two tasks in five aspects (English oral proficiency, topic development, fluency, range, and accuracy). It also showed that a monologic task resulted in lower achievements in those five aspects. In the comparison of the correlations with English proficiency, the range reached the top in both tasks, followed by topic development. The study provides some helpful information regarding which types of speech tasks and linguistic features of EFL oral proficiency are more desirable for targeting in teaching and assessment.