The purpose of this mixed-method study was to analyze the most frequently occurring errors of college students in order to know their weaknesses and appropriately address them. The corpus was composed of 78 essays written by students taking up Speech and Oral Communication class from business, nursing, and education programs. Errors were initially identified using Grammarly, a grammar and plagiarism detection software, supported by manual editing done by researchers. Errors were classified using the headings and subheadings provided by Grammarly, although other categories not captured by the software were added by the researchers. Results showed that the most frequent errors committed by students were on grammar, punctuation, and style. On grammar, the top three errors were verb errors, determiners, and wrong or missing preposition. On punctuation, prevalent errors were found in compound-complex sentences, followed by comma misuse, misuse of semicolon, quotation, and other marks. On style, wordiness was common in many sentences. Such writing difficulties encountered by college students give an implication that English teachers should put more emphasis on grammar, punctuation, and style in their teaching. Thus, a yearly English diagnostic test for students is strongly recommended to identify their weaknesses and apply the appropriate remediation needed.