Abstract: The invention provides mutant or variant oleosin polypeptides having one or more amino acid substitutions, particularly one or more arginine substitution for lysine, and having one or more amino acid deletions. The mutant oleosin polypeptides provide for higher triacylglycerol compared to wild type oleosin, including when the mutant oleosin is expressed in plants. Also provided are polynucleotides encoding the mutant oleosin(s), constructs and host cells comprising the polynucleotides, methods for producing oil bodies comprising the mutant oleosin(s) and for producing oil in host cells and plants. The invention also relates to plants, particularly transgenic or recombinantly engineered plants, expressing one or more of the mutant oleosin polypeptides, as well as seeds and oil bodies derived from the plants.