Similar to other Web 2.0 platforms, user-created content on question answering (Q&A) sites raises concerns about information quality. However, it is possible that some of these sites provide accurate information while others do not. This paper evaluates and compares answer reliability on four Q&A sites. Content analysis of 1,522 transactions from Yahoo! Answers, Wiki Answers, Askville, and the Wikipedia Reference Desk, reveals significant differences in answer quality among these sites. The most popular Q&A site (that attracts the largest numbers of users, questions, and answers) provides the least accurate, complete, and verifiable information.