Abstrak This research aims to explore the forms of commissive expressions and how they are employed by the characters of the film in accordance with the contexts of situation where the commissive expressions occur. This is a speech act research that employs a descriptive qualitative method. The source of data is a film entitled “Harry Potter and the Goblet of Fire.” By using a purposive sampling technique, the researcher finds 36 data of commissive expressions in the film transcript. After the data have been collected, they are analyzed based on the domain of the dialogue and the researcher uses SPEAKING formula as the guiding theory. Each datum is analyzed further to know the contexts of the situations of the dialogues where the commissive expressions occur. The findings of the research are as follows: first, the researcher finds six forms of commissive expressions in the dialogues of the film “Harry Potter and the Goblet of Fire,” they are promise, refuse, agree, offer, oppose, and threat; second, all the characters employ commissive expressions both in formal and informal situations and the domains found are school domain, friendship domain, family domain, public place domain, and graveyard domain. The characters use high intonation if their relationships are less intimate and they use usual or low intonation if their relationships are intimate. Finally, the researcher hopes this thesis will be useful for the English Department students and the other researchers. The researcher also expects that the other researchers will be interested in conducting a further research about speech act.