Provided are isolated polypeptides comprising the amino acid sequence at least 80% homologous to SEQ ID NO:68, 51-66, 69-100, 379-656, 707-715, 720-723, 742-754, 764-771 or 772 with the proviso that the amino acid sequence is not as set forth by SEQ ID NO: 765 or 771, isolated polynucleotides comprising the nucleic acid sequence at least 80% identical to SEQ ID NOs:18, 1-16, 19-50, 101-378, 657-672, 674-706, 716-719, 724-741 and 755-763 with the proviso that the nucleic acid sequence is not as set forth by SEQ ID NO:756 or 762, and isolated polynucleotides selected from the group consisting of SEQ ID NOs:779-792 and methods of using same for increasing oil content, yield, growth rate, biomass, vigor, abiotic stress tolerance and/or nitrogen use efficiency of a plant.