| Overton | Win. W. | Farm Rocks Spring, Southern Brook | OV4 | 1924 |
| Overton Bros. | - | Jam Hills and Minipree, Bruce Rock | K3K and 16D, 45E | 1962 |
| Owen | C. S. | 27338, South Kumminin | 0SC and 12C, 120A | 1962 |
| Owen | E. | Rosedale, Pickering Brook | 0EO | 1912 |
| Owen | E. | Rosedale, Pickering Brook | 0EO | 1924 |
| Owen | Eva Ellen | Adelaide Park, Picton | 9OO | 1924 |
| Owen | H. H. | Shannons, via Katanning | H4O | 1912 |
| Owen | H. H. | Shannons, via Katanning | H4O | 1924 |
| Owen | John | Cambrian, South Fremantle | H0E | 1912 |
| Owen | John | Cambriau, South Fremantle | H0E | 1924 |
| Owen | John | Lots 152, 155, 154, 177, 184, Korijekup Estate, Harvey | ZJ0 | 1924 |
| Owen | R. C. | Ptn. Canning 75 and Avon 1771 Lots, Pickering Brook | 0EO and 13C, 15A | 1962 |
| Owen | R. J. | Roebourne | RO9 | 1912 |
| Owen | R. J. | Gwalia Farm, Welsh Settlement, Coomberdale | 8TO | 1924 |
| Owen | Tudor H. | Common, Broome | 5TO | 1924 |
| Owen | W. L. | Minnawarra, Armadale | 5LO | 1924 |
| Owen | W. L. | Brimscombe, Donnybrook | O8L | 1924 |
| Owen & Beit | - | Mount Erin, via Geraldton | O2B | 1912 |
| Owen & Beit | - | Mt.Erin, via Geraldton | O2B | 1924 |
| Owen & Co. | F. H. & C. | Mininup, Jingalup, via Kojonup | F0E and 58F, 38C | 1962 |
| Owen-Daintrey | - | Moreland, East Brookton | D1N | 1912 |
| Owen-Daintry | - | Moreland, East Brookton | D1N | 1924 |
| Owendene Farmers | - | Owendene, Darkan | A1W and 11B, 13A | 1962 |
| Owens | L. | Ingersly, Pingrup | LO2 and 1C, 106A | 1962 |
| Owens | N. F. | Nelson 9353-4, 10837, Manjimup | 4DK | 1962 |
| Owens | R. J. | Nelson Loc. 9871-2, Northcliffe | 4RO and 80D, 30E | 1962 |
| Owens & Sons | L. R. | 2746-7, 6082, Lake Toolbrunup, via Tambellup | 1LO and 22B, 111E | 1962 |
| Oxania Co. | - | Oxania, Katanning | 9JF and 14B, 49A | 1962 |
| Oxenham | Chas. | Mt. View, via Northampton | O5X | 1924 |
| Oxenham | Richard | Malgaroo, Lower Murchison | 7RO | 1924 |
| Oxenham | Richd. | Malgaroo, Lower Murchison | 7RO | 1912 |
| Oxenham | T. | Block 39, Oakabella | T1O | 1912 |
| Oxenham | T. | Block 39, Oakabella | T1O | 1924 |
| Oyston | Francis Jas. | Glen Millan, Baker's Hill | F6O | 1924 |
| Oyston | L. E. | Glen Millan, Bakers Hill | 0LE and 41B, 46A | 1962 |
| Oyston & Son | H. A. | Hilston, Bakers Hill | 1OY and 12B, 71A | 1962 |
| Ozanne | Eric Murray | Preston Agric. Area Lot 46, Donnybrook | 3QK | 1925 |
| Ozonne | C. | Bridgetown | C0Z | 1912 |
| Ozonne | C. H. | Bridgetown | C0Z | 1924 |
| P.M.G. Lines Training School | - | Dunreath, Guildford | PM6 and 24B, 21E | 1962 |
| Pabst | Sarah Fanny | Emu Farm, Doodlakine | M7P | 1924 |
| Pacak | J. | Lot 666, Bassendean | ZN1 | 1962 |
| Pache | J. B. & H. B. | Bellrock, via Kunjin | K4P | 1924 |
| Packard | E. & B. J. | Hay Loc. 882, Frankland River | 8GP and 25D, 18E | 1962 |
| Packard | John | Rockdale, Bruce Rock | 8PZ | 1924 |
| Packard | R. T. | Mount Kokeby | RP6 | 1912 |
| Packard | R. T. | Mt. Kokeby | RP6 | 1924 |
| Packard | W. J. & D. R. | Girrawheen, Katanning | P4Y and 17D, 104E | 1962 |
| Packham | F. | Locs. 10 and 15, Tammin | 0PX and 2C, 6E | 1962 |
| Packham | Frank | Locs. 10 and 15, Tammin North | 0PX | 1924 |
