Compositions related to the quantitative trait locus 6 (QTL6) in maize and methods for their use are provided. The compositions are novel molecular marker loci genetically linked with QTL6 and which are associated with increased oil content and/or increased oleic acid content and/or an increased oleic acid/linoleic acid ratio of a plant. These novel markers are characterized by the presence of at least one polymorphism relative to the corresponding marker locus from the QTL6 region of non-high-oil, non-high-oleic acid maize plants. In some embodiments, the novel marker loci comprise coding sequence for a maize DGAT1-2 polypeptide or biologically active variant thereof. The marker loci of the invention, and suitable fragments thereof, are useful in methods for manipulating oil and/or oleic acid content and/or oleic acid/linoleic acid ratio of a plant, for marker-assisted selection of a plant, and for marker-assisted breeding of the high oil and/or high oleic acid trait.