Document the entire list of authors the first time a source is cited in the text of your paper. This information can be provided at the beginning of a statement, or provided in parentheses at the end of the sentence: "According to Smith, Jones, Johnson and Brown (2011), ..." or "(Smith, Jones, Johnson, & Brown, 2011)." For all subsequent citations of the same article, use the first author's name followed by et al: "According to Smith et al. (2011)..." or "(Smith et al., 2011)."
Cite multiple works by the same author listing the author's name, followed by the dates of his publications: "According to Smith (2005, 2011)..." or "(Smith, 2005, 2011)."
Designate multiple works by the same author in the same year by allocating a suffix to each document. Refer to the alphabetized reference list and assign the articles by one author a letter, in consecutive order: "According to Smith (2011a, 2011b), ..." or "(Smith, 2011a, 2011b)" or "(Smith, 2005, 2011a, 2011b)" for multiple documents from multiple years.