This study aims to determine individual and process differences that influence argumentative writing with multiple texts. The participants of this study, which used a predictive correlational design, were 101 high school graduates and undergraduate students from two provinces in southeastern Turkey who voluntarily participated in the study. The data were obtained from argumentative essays written by the participants after reading source texts, as well as from a topic interest scale. The participants read five different source texts with different claims related to climate change and global warming, and then they wrote argumentative essays evaluating the claims in these texts. Pearson correlation and hierarchical regression were used to analyze the data. Generally, findings indicated that students were not sufficiently successful in argumentative writing with multiple texts; both demographic characteristics and certain individual variables affected composition length. Topic interest, composition length, source content citation, and addition frequency variables accounted for approximately 41% of the variance in text-based argumentative writing. The findings of the study highlight the variables that are effective in text-based argumentative writing tasks and discuss them within the framework of the multiple-text literature.