This study contributes to research on source integration in argumentative writing, with a focus on the understudied aspect of source choice and use in counterarguments. Using source-based argumentative essays written by 13 students in one English as a second language section of a first-year composition course in the United States, the author examined the types of sources related to confirmation bias as cited by students in counterarguments. Analyses of the essays included observing students' stances on the issues; identifying the counterarguments; classifying the sources as confirmatory of students' stances, opposing, neutral, or background; and counting the number of citations. The findings reveal that the students mostly cited background and confirmatory sources when writing counterarguments. Insufficient citation was evident in both counterarguments and entire essays. Pedagogical implications include guiding students toward reading and integrating opposing sources to potentially improve the quality of counterarguments and to promote perceptual gains beyond the classroom as students write about social issues important to them.