Argument skills play a crucial role in fostering students' scientific literacy. Students who possess such skills can employ reason and evidence to make decisions. This classroom action research was aimed at investigating the best practices for teaching chemistry to promote argument skills through socioscientific issues (SSI). The participants were 46 Thai students in Grade 12 (students aged approximately 17 years old) studying petroleum chemistry in the first semester of the 2014 academic year. To research my own teaching, I collected data from classroom observation, my reflective journals, the students' reflective journals, and an argument skill questionnaire (ASQ). Debating on petroleum-related issues helped the students to practice and improve their reasoning skills, and it showed them the importance of using evidence to formulate a reliable argument. The competition to answer questions in class also allowed students to practice reasoning. Finally, the ASQ results indicate that teaching through SSI can improve students' argument skills. The implication of the pedagogy of argumentation in science classroom is discussed.